I love, love, LOVE CAS, it truly is it's best in 4 (minus one notable exception...) and between walkstyles, accessories, skin details and the like, I can spend literal hours* refining a sim's look to represent a sim's personality, even if some of my own choices strike me as a bit obvious (like, what alien would actually wear an alien t-shirt? ...unless they intend to throw everyone off!). In particular, I like assigning walkstyles based on personality, so I have a bunch of erratic and goofball sims with the goofy walk, and snobby and materialist sims with the snooty walk. I ADORE seeing my simmies out and about, strutting their unique walks (not so unique after making so many sims, but, what can you do? *cough*AddMoreWalkstylesAlreadyMaxis*cough*) and it helps me remember who's who ("Oh right, he's my comedian! That's why he walks like that...").
I also really like playing against type. I have one sim whose hotheaded, mean and evil... and is the cutest pink-clad sim around, down to her perky walk and high-pitched voice. There's also my big bad werewolf (totally not just a rebranded vampire, nope :|) guy who looks mean and has a tough walk, but is really just a big sweetie and wants to make friends.
*I've had it take literal weeks to create certain sims because I want so desperately for every part of their look to come together to really hint to their personality. I might have a problem...
