I always leave them as they are, with the exception of things like skin details in saves that I have CC in, which is only a couple of my games. Generally speaking I leave most things to chance when my sims procreate. I have a mod that causes traits to be randomly chosen, I try where I can to let sims choose their own partners based on autonomous actions towards others and I use random generators to decide other things. I find that this creates much more interesting gameplay and gives me chances to experience gameplay I might otherwise not see.