I do most things myself, but a regular check (e.g. once a year) will reveal problems which you didn't know about, and is important to get expert checkup.
I was wondering about a creak for a month before I dared ask the bike shop, and he soon convinced me that "the tighter the better" policy I was using on my bolts, was not neccessarily correct. I had an overtightened aheadset, crushing the ball bearings. No lasting damage thankfully.