I have played with expo on my planes, and in general don't use it.

One plane I use it on all the time is my combat Gremlin. It's got a Supertigre 45 and goes like stink. It's also got 2" aileons, so doing a full throttle inverted low pass makes it sensitive as heck to control input, not to mention making the pilots knees knock! When I programmed about 40% negative expo in it, it made it fly like a much more solid plane.