Some have reported that among the Platinums scheduled to stay at a property on a given night, rate paid determines the order in which upgrades are pre-blocked. Don't know if that's true, but it would seem to make sense.

The other advantage, of course, is that if the hotel is full and no upgrades are available at all, you may be stuck with the room you booked. If you book a "spectacular" room, you should be assured of at least that.