Yep.

I have on the fittings that I have had. Took my whole bag. It's not just about whether or not there are distance gains. Perhaps more importantly, you can see whether your dispersion is better and by taking your wedge(s) and last hybrid/fairway(s) you can make sure they fit in with those clubs for gapping.

Michael,
The fitter will get you to hit some with your bats to benchmark your distances, left/right, launch, spin and such stuff, to compare against the available options. It provides the data basics.
Just go into the process without preconceptions and be prepared to experiment.
Let's face it - when do you normally get the undivided attention of a golf pro intent on finding the best clubs for you???
Enjoy
JT

Thanks for your replies guys