Disney will transfer luggage to the swan and dolphin and the S/D will also transfer luggage to a Disney resort - we have done this many times in both directions. Keep in mind that your bags won't arrive until at least check in time but other than that I find it a great convenience. We pack a day bag that can fit in a locker or be carried, hit the park of the day and then return to the new resort after 4ish to check in, grab our bags from bell services and get settled.