Depends....
on what is included in the "fitting". I had this done over the winter at Bicycle Ranch in Scottsdale, AZ. I ended up spending two hours with a USCF certified coach who analyzed not only my bike, but also me: flexibility, ergonomic issues, any comfort problems, strength issues, pedal stroke, etc. It also included videotaping and some referrals and suggested exercises (I needed to improve core strength).
The result? We dropped my saddle height pretty dramatically. This helped with a perceived leg discrepancy in my pedal stroke and kept my hips straight ( I had been reaching too much). He also emphasized that this should help smooth out the power delivery in my pedaling. Also changes were made in bar/stem height to help with some back issues that I occasionally encountered.
Now, about four months later, I can say that it was absolutely worth it. I've observed pretty significant increases in power output (Powertap) compared to last season. My first race is in a week and a half so I'll know better soon.
Basically, it comes down to how confident you are in your bike setup (obviously I wasn't), what level of services are offered, and how serious you are on improving.