mishoe is correct - it is only good for your hotel stay unless you have a Land/Sea package. We had both scenarios:
1st night POP - single, 1 night KTTW
Next 3 nights POLY as Land/Sea - KTTW for ship and cruise issued
Cruise 4 nights - same KTTW as POLY
Returned to POP for 2 nights - new KTTW issued (though they did add our remaining park days on the new KTTW).
That being said, we did have numerous problems with our Keys - my parents, dh and 3 year old nephew all had to have keys re-issued at one time or another during the Land/Sea portion.