It is a waste of time to discharge modern battery packs, except to test their capacity through some scientific means from time to time (e.g. a computerized charger/discharger that monitors mAh). NiMH packs and modern NiCds do not develop a memory, and there is no appreciable degradation from leaving them sit charged.

Holding the throttle down, also known as extended static running, is a bad thing to do to your airplane's power system. Most electric airplanes are cooled by the forward motion of the plane through the air. Without that cooling, the motor, batteries, and electronics can overheat and become damaged. The propeller does little to cool the motor and other electronics, as they are generally located near the center of the propeller's disc, where the least amount of air is flowing.