are you sure about that? we used to take a 1% fuel penalty for leaving the autothrottles on in the DC-10 during cruise. The reason for this is the autothrottles "hunt" for airspeed and are constantly moving the throttles back and forth, as opposed to manually setting power you leave the throttles where they are and its more efficient because the engines arent spooling up and down. however the PMS (performance managment system) equipped 747 didnt have this problem because it would actually allow the airplane to climb or descend up to 100 ft before it attempted to change the power setting. this was a huge fuel saver believe it or not.