Roasting/Baking uses the air, or convection, to transfer heat to an ingredient. Your oven provides this cooking method, and is used because of its highly-accurate temperatures and ability to cook evenly for longer controlled periods. Large items are usually cooked, or items requiring even cooking. The browning it provides is a desired effect of roasting, and enhances the flavors of most foods. Using a convection oven is a bit different than a conventional oven. A convection oven uses a fan to move the hot air around, promoting more even cooking and causing the product to be cooked faster.