When do you start playing a new sim?

I play rotationally and I don’t really have any rules on when I rotate. I switch when I get bored, sometimes I wait until they hit certain milestones. And I’m constantly getting ideas for new sims I want to make so I frequently add new sims to the save. And sometimes if I get really tired of a household and don’t see myself wanting to play them again I just mark them as unplayed and they become townies in my save.