I'm sure its not noticable, but i'm willing to bet it stabalizes the binding a little bit. If you don't land perfectly center, you will have more weight in a different direction, left side, right side, whatever it may be. If its just the metal on wood it would probably put more stress on the ski. The small plastic park would absorb the additional pressure and help reduce the wear on the binding. I doubt it would be noticable, but it probably is still helpful.
And I'm by no means speaking with any factual backing to that, just thinking logically of what may be a possibility.