Well, I don't think there's any ground handling savings...the plane still arrived, the BA staff would still be paid, and the catering costs would've just been shifted from the cancelled flight to the flight that ran.

What definitely would've been a cost to BA is any disruption costs, i.e. putting people up in hotels in LAX if they missed connection, loss of the good will of passengers who expected to be on flight "A" only to be delayed onto flight "B".