Disney is pitching it as a way to reduce the amount of time it takes you to get your welcome packet and room keys when you first arrive at your resort. You enter on-line most of the same information the CM at check-in would do. When you arrive at the resort there should be a special desk/kiosk for those that did on-line check-in. There they will have your welcome packet that contains your room keys, resort information and dining plan information (if on a dining plan).