With platform pedals your pedal stroke is 1-2. You push down with your right foot pressing down on the sole of your right shoe, then you push down with your left foot pressing down on the sole of your left shoe and you repeat this over and over.

With clipless there is no 1-2. You whirl your feet in a constant circle. When you really have it going good you are not applying preasure on the shoe at all. Just one long WWWWHHHIIIRRRLLL.