If you are riding powder, the rocker in the nose helps lift the board back to the surface and the camber in the tail faltens the board out so that you maintain speed. If you have full rocker (tip and tail) the there is no counter pressure in the tail when the nose lifts, the board keeps rising and the tail drops creating drag...think of a old school roller blade break. It is not a huge hinderance (the full rocker that is) but if you are in powder a lot than S-Rocker (or any rocker in the nose and camber in the tail) is worth it.
Oh so if you're on a plain rocker and are going at really high speeds, will your lead foot rise a lot higher? Perhaps making you like "skip" on the snow?