What is the difference between HEAT DRY and AIR DRY options?

With the HEAT DRY option, air inside the dishwasher is heated during the dry part of the cycle. With the AIR DRY option, the air is not heated, which helps save energy, but dishes take longer to dry (overnight) and some water spotting may result. Some items such as plastics may need towel drying when using AIR DRY. (Page 9)