Here's why:

* Potentiometer: A potentiometer is a variable resistor, meaning its resistance can be changed by turning a knob or dial. In the case of a volume dial, turning the knob changes the resistance of the potentiometer, which in turn controls the amount of electrical current flowing through the audio amplifier. This ultimately determines the volume of the sound output.

While there are other ways to control volume, potentiometers are the most common and practical choice in stereo systems due to their simplicity, reliability, and affordability.