Why is automatic level control (ALC) used with an RF power amplifier?

Automatic Level Control (ALC) is a feedback system in a transmitter that monitors the output power and reduces the gain of earlier amplification stages if the output tries to exceed a safe limit. Its primary purpose when used with an RF power amplifier is to prevent excessive drive. Overdriving an amplifier can cause the signal to distort, resulting in poor audio quality and generating wideband interference known as "splatter." ALC keeps the amplifier operating safely within its linear range. While ALC prevents distortion products, it is not a harmonic filter, nor does it balance audio frequencies or increase amplifier efficiency.