I can spend an hour perfecting my Sim's look, and usually set one outfit per category. Some Sims get an additional outfit if their story requires it, but generally I treat them like cartoon characters and what they wear is what they wear. I'll update them for life changes like aging up, marriage, having children, or career switches, but often keep their original outfit as one of the extras for nostalgia. It bothers me when they auto-change into something that's not their main outfit!