Originally Posted by
Thetank
It teaches you a better pedal stroke on freewheeling bikes. I found my road bike rides much more effective after I started riding fixed.
Since the pedals never stop moving, it can also teach you to have a lazy stroke too. I gave myself a dead point in my stroke after I first started riding fixed, because I could just let the legs go limp and the pedals would end up where they belonged anyways.