In the words of JHS Pedals:

With a name like the JHS Pedals Mute Switch, it doesnt
take a rocket surgeon to guess what this little guy does. But in case
youre still curious, its a switch that mutes your signal. This
latching design lets you immediately cut your signal for silent tuning,
breaks between sets, and more. Wed love to go on about this valuable
tool…but weve pretty much covered it.

It turns your signal on and off

This Mute Switch mutes your sound. Its that simple. And yet we think
that with its color-changing LED indicator, high-grade components, and
convenient compact size, the JHS Pedals Mute Switch does it better than
any other.