To cut off the final amplifier during standby periods
To keep the carrier on frequency
Explicación
Stray feedback through the internal grid-to-plate or drain-to-gate capacitance can return enough in-phase energy from output to input to make an amplifier oscillate on its own; neutralization injects an equal, opposite-phase signal to cancel that feedback. It has nothing to do with keeping the carrier on frequency or with standby switching.