That way you won’t forget to remove any mods or custom content when you play the Apocalypse and won’t forget to put them back in when you go to play your non-Apocalypse games. If you wish to use mods or custom content in your Apocalypse save as well as your non-Apocalypse saves, we highly recommend generating a brand new Sims 3 folder (rename your original one and load the game, a new folder will be generated).
Use Mods and/or Custom Content at your own risk.