I have a specific save in which I play rotationally with premades and other Maxis made Sims that I've added into the world.
I'm not into the lore, I just play the way I want to.
Bella Goth has an affair with Don Lothario and had a daughter with him, Mortimer thinks she's his child. Bob and Eliza Pancakes had twin daughters and other one of them is transgender. Sergio Romeo came out of the closet when he fell in love with Gunther Munch and he broke up with Siobhan Fyres. Sergio and Gunther are living together now and Gunther wants to adopt a child but Sergio hates children.
I also play with just Goths on another save. I'm planning to make Alexander a powerfull spellcaster when he grows up.
I had a save with Don Lothario who had children with most of the females, but the game culled the majority of them, so I ended up deleting it. I continued playing with some of his children in another save, but I deleted it also later.
Another way I use premades is that I use them as spouses for my own Sims sometimes. My favorite Sim is married to Summer Holiday and their daughter is married to Alexander Goth. My not so berry challenge mint Sim is married to Joaquin Le Chien. Some other Sims of mine are married with Zoe Patel, Johnny Zest and Don Lothario, one is also having an affair with Bob Pancakes.