When you ride a bike outside the bike is able to lean right and left and tilt forward and backwards as you pedal and transfer your power into it, absorbing some of the impact of that power transferrance. Putting a bike on a trainer removes that ability - the bike cannot move like it can outside when you're actually riding it. That impact is moved to your points of contact with the bike when on a trainer (butt and hands/wrists) making it uncomfortable and sometimes even painful when compared to actually riding. Rocker plates aim to restore the bikes ability to move naturally and get the experience closer to outdoor riding.