I just want to say thank you for taking yourself out of the applicant pool to the other schools now that you know where you are going. I think some people just want to see if they can get in places and don't consider that they are actually taking someone else's spot by not telling the school that they will not be coming.
not to say that the OP isn't a fabulous person, but he applied ED it seems, since michigan says he NEEDS to withdraw apps in the next month. difference between that and withdrawing for the sake of other applicants. granted, the OP applied ED, which means he loves michigan. so if he had gotten in under regular admission, he may well have withdrawn other apps anyway, knowing he'd go to michigan.
Does withdrawing do anything for you? Or does it just let other schools know that you're fabulous and they need to keep their hands off?
it doesn't do anything for you; it might do something for other applicants, because schools might be able to give what would have been your spot to someone else. if you apply early decision and get accepted, that school requires that you withdraw all your other apps, since you're required to go there.