You should probably keep your project files and these autosaves on your startup disk in your User’s documents folder… or keep the autosaves on another drive if you want… but keeping them on the media drives in theory might slow down the drives. These files are smallish and constantly are being rewritten and trashed… so media files could be fragmented a bit more if autosaves are kept there.
The Autosaves are backup copies of your project file.
Jerry