It would be used to game the game...
Pilots in fighters would go into a fight full, then as soon as the see a spitfire dump all but 10%, banking that they'll out-fight the spitfire because they're empty.... For the next 4 minutes that they have gas for. Once the spit is dead they'll ditch and repeat.
Bombers will climb to 30K on 25% fuel, then dump 24% of that to skyrocket up to 45K and still have enough gas to cruise across the map and back.
While some aircraft had this historically (SOME, not all), its use in AH would only be to bend the rules to the fuel-dumper's advantage.