Okay, the only backup save I will keep for each character is a save just before they tackle the endgame. Such as before the Military Base and Cathedral in the first game or the Oil Rig in the second game.

Should I only save my game in a new slot when I enter a town, or should I save when I enter a new location in the town? When I start a new quest? What are some other good times to save a game in a new slot?