My feeling is that they offer the transfer during times of high-occupancy at TTR. We have been offered it with each of our stays and have politely declined each time. In June of '14, we said, "If you want to move us and 100 of our friends, we might take you up". Yeah, that was the last time they asked us on that trip.
In April 2015, upon arrival at TTR, we were offered 1 night at Desire RM and took them up on it.. was actually a nice change for our travel day. I had been before but my girlfriend had not. We enjoyed the hot tub, some late night drinks and a good nights sleep but we were happy to get to TTR around noonish the next day.
We are going to be back there for Halloween. Fourth time to DRM, twice to Cabo but just wondered if they were still doing it. Not sure if we would switch, but maybe for a night or two. Just as long as we are back for the Boobs Cruise