WHY COOKING A LARGE ROAST ON A RACK IS SO IMPORTANT?

When large roasts are placed directly onto a pan, as the pan heats up, the heat of the pan will leach moisture out of the roast. And as fat from the meat renders, believe me, the Convection fan can do a good job of splattering all that fat around the oven. You will also find placing the meat on a rack makes it much easier to remove the meat from the roasting pan once it has finished cooking.

Placing a Sirloin on a rack