As some of the later posters here have said, what you will gain is pedaling efficiency. Your body will adapt to only using the muscles needed to propel that part of your pedal stroke, then relax completely. We ought to do this all the time, but we rarely actually learn to do so unless something hammers into our bodies the need. Rollers do! Riding fix gear down fast hills does also! Unless we can be completely smooth, both of these activities are scary/close to nightmarish/far from fun. If we stick with it, our bodies learn. And we reap benefits from it every time we get on any bike. Longer, harder days become easier and more fun. We may have fewer chronic injuries.

I spent one winter on rollers post accident many years ago. I have been riding fix gears ever since. I have done nothing else (coaches, etc) for my pedaling style but have heard more than once that I pedal very smoothly, once hearing that in the late miles of a hard fix gear ride.

Ben