Sorry, I realized this was an unclear question, but I got it answered.
I meant the service of "Resort Check In" where they check your bags at the hotel for your departure.
Resort Airline Check-in is often confused with Disney's Magical Express. They are related but separate services.
First off, only people flying on certain airlines (called "participating airlines") are eligible to use RAC.
RAC allows users to check in their luggage at the resort rather than taking the luggage to the airport. You also check in for your flight and are given your boarding passes. RAC is run by a subcontractor and must follow TSA's rules. Checking in is EXACTLY the same as at the airport. Everyone in your party (18 and over) must be present and show ID.
Once you check in your luggage with RAC, you won't see it again until it's on your home airport's baggage claim carousel.
Each resort's RAC desk is open from 5:00 a.m. to 1:00 p.m. By TSA regulations, luggage may be checked in no earlier than 12 hours prior to flight time, and no later than 3 hours prior to flight time. So, for example, if your flight leaves MCO at 7:00 a.m., you can't use RAC.
I've read numerous stories about occasional long lines at RAC. To protect yourself, make sure you do this checking in way ahead of time, so you don't get delayed going back to the airport.
When you use RAC, you can get yourself back to the airport any way you'd like. You can take the Disney's Magical Express bus (which you need reservations for) or any sort of private transportation, it makes no difference.
I hope this answers all your questions, but please post back if there's anything else you need to know!