For the Centurion program in the UK, the room is upgraded at the time of the booking - so I if I book a room type, I am charged the rate below for the room category one level down. As the others have said, not all rooms have a FHR rate.

Sometimes a property will do a further upgrade when you actually check-in, but that is entirely at their discretion.

I booked a City Suite at the Singapore property (and paid for the level below) - so 550SGD/night in Dec - and that was the room I got.

Tokyo, booked Mandarin Corner room, and ended up with an Oriental Suite.

KL, Executive Park View. Paid for the level below and hotel gave us access to Club floor.

Landmark MO, L600 Premier, paid for a L450 Deluxe.

Sometimes though, the price delta between the 2 levels is tiny so the upgrade benefit is't that great. It might be the same room size, just a few floors higher.

Overall though, the MO benefit is the standout benefit on Centurion.