IMO...partitions are created to give more order to a hard drive, particularly now that hard drives are so enormous in terms of capacity. As long as hard drives were small (less than 50GB), it did not really matter if everything was stored on one partition...disk maintenance was easy enough, did not consume extensive time, and it was pretty easy to keep good order on a small hard drive. At that time, backups were generally stored on external media and not stored on a hard drive.
With the advent of larger capacities...video files being stored/saved...more knowledgeable users with diverse interests...storage capacities developed became used more by those owning/using computer systems. Types of files and sizes of those files stored...increased for many users. Partitions became a convenient mechanism for isolating a particular type of file...for easy access order.
Partitioning a hard drive will not necessarily result in the ability to access data on another partition...if the drive is defective/failing. But it might provide a very thin chance of such, if one assumes that damage/defect is restricted to a given area. IMO, this has not been proven to be the case for many hard drive failures. IMO, a better approach would be multiple drives where, logically, a disaster on one drive has no impact on a different drive.
I have a 2TB and a 3TB drive on this system, with multiple partitions on each for storing everything from videos to backups. I have my O/Ses (dual-boot) and programs installed on a totally separate SSD. I've never liked the idea of having everything on one drive...but, when I did, I created partitions just so that I could maintain some order and not have hunt for a given group or type of file.