when meat is cooking, the juices force themselves internally to the outer edges of the meat. When resting, the juices will re-distribute themselves throughout. Kinda like back in the day when I didn't know better, would grab a steak off the grill and the first cut would render the plate full of flavorful juice......they didn't have a chance to re-distribute throughout the cut of meat..........I hold and rest briskets and butts at least two hours....extra tenderness will happen to those who wait
and you can have an extra beer or two while you are at it. 8)