Trainers can be used for alot of cool things...

several have already been mentioned, practice aerobatics, make mods, fly it when you wanna do some calm flying, etc.. Some other pretty cool things you can do are... putting floats on it a whole new world, I'm working on this myself. Put a little video camera or still camera on it, you will then appreciate the stability. Bomb drops, etc.. I always view my trainer as a "stable" plane, not worse than my others, but a compleatly different kind of plane.. those are just my thoughts on the subject.

Somehow i missed the post above that says the same thing right on man.