pienut, it is all three in one. WDW uses electronic room keys, it also has your park ticket/ultimate hopper coded onto it, as well as charging priviledges throughout WDW. Depending on the resort, your charging priviledges will vary as to amount. Value resorts $500, Moderates $1000, Deluxe and DVC $1500. ONce you reach your limit, your credit card number that you left at the desk for check-in will be billed, then a new line of credit opened.
At check-in you can tell them if you want all (or none) of the keys to have charging ability.