My decision to foil or not often depends on the butt. If I get one that stubbonly hangs at the plateau, I will foil it. If I need to speed things up to get one done, I will foil. Obviously those two often go hand in hand, but not always. Sometimes, I just need to cook the butts quicker. When time is a factor, I had much rather have the extra time for the butts to rest foiled in a cooler than sitting naked in the smoker. IMHO, the real magic & secret to a moist, tender, flavorful butts happens during the resting stage. I try to allow at least 1 hour for resting but more is much, much better.