Autosaves and quicksaves are one-time use. They are overwritten with the next autosave/quicksave. Manually saving and overwriting a save is better for many reasons, a big one being that they are not overwriting the same file over and over again which can lead to corruption.
The same response I always provide (for the most part):
I keep all my saves and manually save about every 5 minutes for backup reasons, wanting to go back, and so forth. Whenever I hit around 105 or so saves, I archive all but the most recent 5 and put them into a 7z archive with maximum compression since the 7z format is both open and gives generally the best compression ratios. I keep all these archives in a separate directory and number them so I know which saves they have.