There are occasional incidents where the Crew bunks are inop and they have to have horizontal rest in the Club cabin - if they never achieved this then then flight would not be able to go!
Actually, there isnt a single scheduled sector on BA where no horizontal rest would put the cabin crew out of hours. Any rest seat (economy even) in the cabin adds enough duty time to make our longest sector legally without discretion. (SIN-LHR 14hr45 FDP, max allowable for cabin crew = 14 hrs. 3 hrs in seat = 1 hr extension = 15hrs to save you looking it up)