Duty Travel
I hadn't realised until recently when I quizzed one who actually sat on the FD that Duty Travellers can request the jump seat, if I'd known then I wouldn't have given it as I don't believe that is a proper use of the privilege. A duty traveller is not going to get in trouble if the flight is full and they don't get back for duty; if the company thought their travel was urgent then they would get on somehow.