We have a local company that we trust do them yearly, sometimes twice (spring/fall). Yes, they can catch things, for good or bad, and keep things clean, for a tiny bit of efficiency. I'm sure some will say you can DIY, but that's not in my realm.
If things go to pot on the hottest/coldest day of the year, you're usually at the top of the list for a repair visit.
I would check with friends/neighbors before I'd go with the big guys, though. We've run through a few companies who will send out just anyone. Our current company has two techs, and they know our system.
