You do all that for a couple of reasons. The main one is so that the juices will settle back in to the meat. While that is happening, you want to keep the meat warm and this is a very effective method of doing that without further cooking the meat.
Dawn gave you a very good answer. I used that method with a 5 pound prime rib for Easter (yesterday). Even though I didn't smoke it, this method worked the same and the meat came out very tender, rare and juicy.