We stopped at the concierge desk and asked for reservations for 1 hr later. They took our name said we had preferred seating. By the time we got to Mythos gave them our name, we still had to wait 1/2 hour for our preferred seating.
So not too sure if it really does any good. Also didn't see any difference in the shows.
Ther place I've seen the biggest difference with showing your room key for dining is the Hard Rock Cafe. We have been there when the line was wrapped around the building. We showed our room key and were put in a separate line and were seated in ten minutes.