As Random Bob intimated, your choice depends on what you want to do. Backup strategies are infinite, from immediate overwrite to once-a-month, retaining all previous versions of files, multiple backup sets, compression, password protected....... Personally I think it's best to save all revisions of documents (some type of incremental backup) unless space is an issue; don't overwrite. Frequent saving of what you are actually working on is an exception.
I got Dantz's Retrospect free with a WD drive. It can do anything you can imagine but it's difficult to understand all its ins and outs. Great, once understood.