As a meat roasts, it releases juices that collect at the bottom of the roasting pan. If the meat rests on the pan, its underside will cook in the liquid and therefore will be cooked by moist, rather than dry heat. The result is unsatisfactory. The meat's underside overcooks before the rest is done because moist heat cooks faster than dry, and conduction from the pan's surface intensifies the problem. Another disappointing outcome of the non-rack roasting method is a mushy, rather than crispy bottom.
** Asian Recipes