After you remove steak from the grill (most meats from the grill actually...except fish) it is not important that it is "cooking" after, but as it slightly cools, the juices redistribute within the meat itself. If you want to cut it, or, "test" it, wait 5 minutes after removing from heat. If you cut it on the grill, or before letting it rest, you just lost all of your juice, and no matter what you do, it will be tough and yuck. Also, for steak, you need to salt the hell out of it and let it come to room temperature before grilling. The salt tenderizes the meat and helps keep the juices in while cooking. Letting it come to room temperature prevents the meat from being raw in the middle, and burnt on the outside.