I like playing generations and through that I may utilize certain family members for new challenges (if I don't devote a whole new save file to a certain challenge--some challenges can be lengthy and need their own file).
I also like to try all the features of a new pack when it comes out, so I'll designate a certain Sim in the family for each new aspiration, kids aging up will get to try out any new traits, then I'll spread the new jobs around, etc. so I have everything covered.
Right now I'm still playing a file I started when Lovestruck came out with a single Sim who married Manuel from the pack. Their family is on Gen 4, and with the descendents I've have played through Life & Death and the Small Business pack features. This save is pretty well populated now, though, and big files can get glitchy, so I think for the Nature pack I may start a new save so I can just jump in with both feet to explore everything faeries and nature in its own file. 😄 It will turn into another legacy, I'm sure, 'cause that's mainly how I play. I always say they'll have one kid, and then next thing I know, there's 7. LOL!!! 🤣