I guess this ties into my first answer of premades with backstories. Lore and history! The Sims have dead ancestors with their own stories and memories. Some of that data is corrupted (no real surprise), but there's still a lot there. A LOT. I used Simpe to fix everything that was corrupted, retrieved graves, replaced missing Sims that were listed in family trees etc. There are so many great grandparents, grandparents, aunts and uncles of current Sims. And some are really interesting. Just in Olive's garden you have several service people, several of her husbands, her sister and her husband, a teenage girl, and the ex-wife of one of Strangetown's current residents. It's so dark and fascinating. I've always wondered about the creator that took the time to do that.
