I was hesitant to use snapshots at first because I didn't understand how they worked, but as the name implies, they're just a copy of your session made at a specific time. Snapshots don't fork your project, so if you load a snapshot, make some changes, and then save, the changes are saved to your main .ardour file -- a save will never update the snapshot, though you can of course make more snapshots if you want to save changes without overwriting your main .ardour file.