It's a Morale boost for us and a hit to their ego for one. Remember that they're fighting under the belief system that "God" is on their side and blah blah blah. So losing their leader should be a fairly big blow against them. Of course someone else will just step into the lead position and they'll probably fight doubly hard for awhile but this shows them that we can find them no matter what holes they choose to hide in in Afghanistan.