The unwritten benefit of course being that a customer in these classes would find themselves right at the end of the list for downgrade or offload, and pretty close to the top of it for DUT. You’ll never see that published, but it’s definitely there.

(For the pedants, yes I know, strictly speaking it’s taken from the FBC not the RBD, to avoid conflict with the generous policy on allowing connections in full-fare classes on a discounted fare, but the principle applies.)