Meat should be rested after cooking so that interior juices can redistribute. Timing depends on thickness. If no residual cooking is necessary meats can be rested simply rented with foil. Briskets need about 20 min (for packers and hefty, less for thin flats); butts need 30-45.
Anything cooked at high heat (whether barbecue or not - rib or loin roasts, whole tenderloins, steaks, whatever) will continue to cook when removed from the smoker, oven or grill. Wrapping these items tightly will intensify this residual cooking because the heat is more contained. Keep this in mind.