This passive volume control with foot switch has multiple uses, here are a few ways it can benefit you:
1. After you set your amp for your lead tone, find the sweet spot for your clean tone by turning the pedal on and lowering the pedal's volume to your liking. Now you can switch between clean and lead tone at the press of a switch, no more searching for the sweet spot with your guitar's volume control.
2. Control your guitar volume hands free. The large knob can be controlled by your foot if you need to make changes while you play.
3. Use it as a mute switch by turning the volume all the way down.
4. If you switch between guitars with passive and active pickups, attenuate the higher output active pickups with the volume pedal.