Perfectionists spend more time cooking, writing or even painting, but what they eventually finish is noticeably better than something created by other Sims. Perfectionists accept nothing shy of perfection.
Perfectionist Sims do most things better than other Sims, but sometimes it just takes a bit longer.
The Sim can paint higher quality paintings, prepare higher quality food and write better novels.
This trait can help Sims becoming better architects. [TS3:A]
Perfectionists can point out the flaws of other Sims in conversation, usually only available in the Mean interactions if a Sim thinks another Sim is being rude.