I rarely create Sims myself. I have given Vlad an extreme makeover so he looks less ridiculous, and I will give other sims minor makeovers (like fixing Christie Sigworth because she grows up looking a bit weird) but mostly clothes/hair and maybe adding a tattoo or other details if a character seems to become part of my legacy and I need them to look their best. But other than my Duchelli legacy founder, I haven't created a single sim from scratch in the entire save, they're all either born in game or generated by the game.
My founder married Don, their Gen 2 daughter married a son of Morgan Fyres/Wolfgang Munch, and they had my Gen 3 heir who then married a granddaughter of Angela Pleasant/Dustin Broke and Michael Bell/Kim Goldbloom. My Gen 4 heir is best friends/in love(?) with Samuel Ward, whose grandmother was the daughter of Judith Ward/Marcus Flex' daughter and Orange Bailey-Moon.
I'm probably going to run out of Sims that I can actually track the lineage of soon, since the original family trees tend to get deleted after a few generations, but it's still more fun for me if my characters get to meet other Sims who have a bit of backstory already, with parents, grandparents, and possible siblings.