The reason in the civvie world for taking off with a precomputed fuel load, doing takeoffs from other positions than the beginning of the runway, and not using full available power is an economic one.
That said I can only talk for fast landbased jets, where the most useless things are the fuel left on ground and the runway behind the aircraft.
Concerning the fuel there were sorties, which called for less fuel due to tactical and structural reasons. It is no good to go into a WVR engagement with three full outboard tanks. Either those stayed at home, were not refueled, or were flown dry with sometimes sensless maneuvers. In the F4 we could refuel the jet without the fuselage tanks 5 and 6, which was used for a quick combat dart sortie over the north sea close to our airbase.