I'm not a HUGE trap shooter. I shoot Sporting Clays and Skeet...But I'm on a collegiate team with many American and International trap shooters. Alot of em have high ribs and custom stocks with combs, and others don't. Just make sure your gun fits you...try out some new things and see how ya like it.
-The high rib allows you to keep your head up and see the bird, it also changes your whole line up so that you can float the bird on your front bead and the shot will go high and break the bird.
-Rasing your comb sets the gun low in your shoulder and raises the muzzle. Combine this with the high rib and your shotgun is all in all angled up towards the flight path of the target.