Each world package deletes the world it states. Completely removes any data associated with it. Any sims living in it, sims currently in it, etc. ONLY thing it doesn’t remove is custom residential rental data. That one is Maxis’ problem but given our knowledge, it’s best to not mess with worlds with custom rentals. Might reduce load. For me saving/loading has become far quicker. Not magical, but better. At least loading into the world menu, lol.
Custom Content is CC that can be downloaded and added to your game
Credit : LunarBritney