I was wondering what the difference between backing up folders/files using drag and drop vs. syncing vs. using backup software to back them up.
The biggest difference will be "automation". It is rather tough to automate backups using good ol' "drag and drop" copies to back up things, while "true" backup software as well as most "syncing" software usually has a way to automate the process (i.e. run the backup on a schedule without you needing to do anything). Some don't like automation, however, as it essentially requires you to leave your backup media (these days most likely an external hard drive) mounted, which means it is potentially susceptible to malware or other things that could mess up you main drive. This is why even if you do some sort of automated backup, it is still good to do a second backup that is NOT automated, thus allowing you to disconnect the drive (and ideally store it off site some where).
Does it make a difference?
I noted the biggest difference between the first option you listed and the other two.
When you talk about "syncing" vs. "true" backup software, then there can be a number of differences.
Generally, with syncing, there is only one version/copy of the "backed up" file as you are "syncing" a copy of the file to another location. On the plus side, syncing generally means you are keeping the file in its native format, which mean you do not really need the backup software to "restore" the file…you can just copy the file from the backup drive or even run the file from the backup drive (not really advisable). Generally, syncing will be "incremental" in nature (i.e. it does not need to copy ALL files each time). The one thing to be careful is that syncing can be a "two way" street…in other words, if set to be two way syncing, then a change to EITHER file will mean a change to the other file…i.e. if you change the backup file somehow, then the original file will end up with that same change. Most syncing software usually allow you to be pick if you want one way syncing (as well as which direction that one way is) or two way.
For more traditional backup software, the first thing to realize is the details will vary by program. Some programs will back the files up to a proprietary file format, which means you then need the backup software to restore the file. Others will use the native file format of each file that is backed up. Backup software will usually offer incremental backups, but they may also offer differential backups (similar but different…more on that below). Some backup programs will offer "versioning" (i.e. save different versions of the same file…useful for example if you are writing the next great novel and find out that the paragraph that you deleted a week ago really was better than what you changed it to and want to either revert to that older version or just pull that paragraph that you deleted out and put it in the current version).
To confuse things even more, there is "true" traditional backups (primary limitation being that they generally cannot backup running processes generally meaning the OS but potentially also programs…they were originally more meant to backup you data, not the OS or programs), image backups (backing up the current state/exact setup of your full volume [either partition or even entire drive], but done to an "image" file on a drive…this means not bootable…you would need to have a backup software running somehow to restore individual files or the whole image), and clone backups (this is essentially making a bit for bit [typically] duplicate of your drive to another drive, which means that other drive will be bootable…although it kind of depends on what the "another drive" is…if an external USB drive where you cannot pullout the internal drive to install in your computer, then you computer must support booting from a USB drive, not something all Windows computers do).
I would guess that using backup software to save files/folders you would need to use the software to recover or view the files/folders?
As noted above, it kind of depends on the backup software. Some will use native file formats of the files meaning you don't need the software to recover/view files, while others will use some proprietary file format. As noted, generally syncing will NOT require the syncing software to restore.
What method takes up the least amount of space on the external drive?
That will be complicated. Ignoring compression, then most likely syncing would be more space efficient, but other methods should be able to match it. Some backup programs will allow you to compress the backup, however. For such programs, this generally means the backup is in some proprietary format, but it could be the most efficient in terms of drive space.
Personally, I would say it generally should not matter unless you have obscene amounts of data to backup as rather big hard drives are pretty cheap. You can get 4 TB external USB drives for about $150 US. So, unless you just have a massive amounts of data, you should be able to go a rather long way with a 4 TB drive no matter how which method you pick.
If recovery is needed which backup method makes recovery easiest?
Kind of depends on how you define "easiest"…as well as what you need to recover.
For individual files or small amounts of files/folders, then using some sort of backup method that keeps in the files in their native format would be the easiest as you just need to mount the external backup drive, find the file(s)/folder(s), and manually copy them back onto you main drive using drag and drop. So, this would be either "drag and drop" manually backups, sync backups, or backup software that saves the backup in native file formats.
For recovering your whole drive, then I personally like cloning. I clone all my boot drives. For cloning, I use external drives that I "build" myself…that is I buy an internal drive and an external enclosure of my choice to put the internal drive in…this allows me to pull out that internal drive from the enclosure if I need to put it in the computer. Then if one of my internal primary drives bits the dust, I just pull out the dead drive and install the clone drive. So, I would be backup and running in the time it takes me to physically swap the drives (5 minutes to 30 minutes depending on the computer). I mainly only do this, however, for my boot drives (i.e. drives that only have the OS and programs…I generally have separate data drives if possible, which is not generally possible for many laptops). I generally have at least one clone of each boot drive that is fairly close to being fully up to date in terms of install programs and Windows/program updates, but might have to do some minor updating.
What advantage if any is it to use syncing vs. using incremental backups?
If doing incremental backups do I need to save the previous incremental backup? I have read that keeping previous incrementals back ups is need and also have read that the previous incremental back up does not need to be saved.
Please make your answers simple to understand.
Depending on the how the incremental backup is done, it may essentially be doing a sync (this is generally true if the backup software saves the backup in native file format). The primary difference is that some syncing software can be "immediate" (i.e. as soon as you make the change, it changes the synced backup copy), while backup software doing incremental backups and some syncing software will operate on a set schedule (i.e. once a day, one a week, once a month, or what ever you set it at).
For incremental backups, then yes, you will need to keep all increments between that last full backup and the most recent incremental backup…basically each increment has a piece of the puzzle. In today's world, this should not really be an issue. Back when people backed up to tape drives or optical discs or even floppy disks (oh, the pain of backing up to floppy disks), then this could be a MAJOR issue if you lost say disk #3 out of the backup set as you would lose any increment of the backup stored on that disk…and maybe even prevent recovering everything else if it was a really badly designed backup program. Now, since people generally backup to an external hard drive, unless you delete something, it should all be in one place.
Overall, backing up can be either simple (i.e. drag and drop copying key, critical files to a USB flash drive or even an external hard drive) to rather complex (i.e. multiple backups using multiple methods and even media).
It might help if you elaborate a little bit on what you are looking to backup as well as about how much data that might entail. With that information, I might be able to offer some specific suggestions.
What I can do is elaborate a little bit on how I do my backups.
My first "line of defense", so to speak, are the clones. As I said, I clone the boot drives on all my primary computers (two Mac laptops…one of which that is used essentially as a desktop…and one Windows computer with multiple boot drive with different versions of Windows). In the case of my Macs, it also means that I end up cloning the data as well. For the one Mac, this is because it only has one drive for the OS, programs and data. For the other Mac, I do have two drives, where one is technically the boot drive (it is an SSD that does still have a little bit of data on it) and the other is the data drive (it is a 1.5 TB 2.5" drive…but it does have an older version of the Mac OS installed on it that I can boot with if needed). For the Windows computer, I use Acronis TrueImage for cloning. For the Mac, I use SuperDuper!, which has a "smart update" clone feature that means it can update the exiting clone drive…so it kind of becomes a incremental backup in a sense.
For the two Macs, the second "line of defense" that I use is Time Machine to backup everything to a NAS on my network (which is a "prosumer" NAS with 4 drives in what is essentially a RAID 5 array…so that kind of gets me a "third line of defense" for the Macs). TIme Machine is a backup program built into the Mac OS. For the one, it runs daily. For the other, I run it manually on occasion (this Mac does not have much critical data that is changed often that is not already backed up in another method…see below).
For the Windows computer, my second "line of defense" is that I use a data drive that is actually a RAID 1 array (aka mirroring) of two drives. So, one drive bits the dust, the other one should still be fine.
For both, I then manually copy (i.e. drag and drop) some critical files to an external drive that is not regularly mounted and can be stored off site. I also will manually copy some files from the computers to the NAS as "manual" backup.
I do also keep some files just on the NAS. For those, I do have some manual backups on other external drives.
You might note that is rather complex and might be way overkill for most people. And I do need to clean some things up, but it works for me.