One thing that hasn't been mentioned yet is that it (obviously) gives you a ground on the plug as well, which is a very Good Thing for computers.
I agree, it's very important
Except that the grounding prong doesn't do a single thing as far as I can tell. Yes, there are three prongs on the wall end of the cord, but only two get fed into the ac adapter (check out the end that slides into the adapter). So, it does nothing to ground the ac adapter.
Ground is actually connected through the metal button that it slides onto.