Sometimes, but not always, the patch will fix something but then break something else. The sad truth is that Sims 3 is a very buggy game. I've owned it since it was released the middle of last year and it's never been bug free. I can't think of specific details of something that was fixed/went bad, but these are some of the current bugs:
1. Can't excavate in World Adventure vacation sites except for spots on a lot.
2. Consignment Shop for Ambitions doesn't always work right.
3. Can't order Omni Plant seeds.
4. Major travel bugs with World Adventures (family tree breaks, unknown children, travelers fail to return home, and more).
I know there are more, but I can't think of them at the moment. Most of the time they aren't game breaking; just annoying to work around. But there's really no way to avoid it because the things a patch fixes really needed to be fixed.