Are your sims Practically Perfect or Fatally Flawed?

I hesitated between "perfect" and "depends"

If it's a Sim I'm going to play a lot, I rarely give them problematic traits, except hot headed now and then. But if they are going to be peripheral sims, I'll throw in a few bad ones now and then.

Question: If you try to re-trait a townie, do the changes usually work for you? Because in the vast majority of mine, the pop up whims and thoughts and emotions etc. still correspond to the old traits they had before I changed them in CAS.