True, the pump is not needed if the fuel tank can be placed in an appropriate position close enough to the carburetor spray bar. But in most planes large enough to require a ST 3000, if the tank is placed on the CG the clunk will be much more than 12" away from the carb. A pump in this situation is very beneficial for insuring a consistent fuel flow to the carb regardless of the attitude of the airplane, or the maneuver it is performing.