I have 6 saves, and every one is themed. For example, one is dedicated to building, and another is dedicated to creating freaks and weirdos. I play 5 out of 6 of those saves in heavy rotation.
Gameplay; there are never any background stories (or families) in my games, my sims live for the moment. If I send a sim to my outdoor club in Windenburg in a blizzard, and people are dancing in the snow (and falling lol), that's the story. It's all about making my sims do funny stuff.
Oh, and as for big saves; I think I have a couple of them with over 50 households?