I play 123 households, ageing off, and with the number always growing. Of course some households I play way more than others. This includes premades, sims I got from the gallery, sims I made, and sims born in the game. One of the reasons why I started jumping households was because the game would randomly assign unplayed sims to fill jobs like bartender and waiter and personally I didn't like seeing Nancy Landgraab working as a bartender when I knew she already had a job. So I went in, gave premades who lost back their original jobs, and left them as played households so the game would instead grab from the pool of endless townies to fill these roles.
I just love world building. It keeps me immersed in the story that I am trying to play out. Everyone has a place, a role, family, drama, basically a story to their name. The moment something happens that I don't like or that doesn't fit in with my save's world vision I have to fix it or get a mod that will fix it. Yes, I am a perfectionist.
I've started a few new saves for challenge purposes, but never from scratch. I'll used saves from other people where the world (lots included) around my sims have already been established. As for my main save, which I started in 2015, that has been mostly built up by me.
Everyone, even the townies, have connections. Be it as friends, family, co-workers, lovers, enemies, etc. Recently, I used a mod to check my total sim count and the total amount was sitting at 1133. And pretty much everyone who spawns receives a makeover too.