In the words of JHS Pedals:

There are two types of players, those that utilize an A/B
box like our Mini A/B here, and those that dont know what theyre
missing. Add one to your pedalboard, and youll find the Mini A/B is
full of indispensable benefits on the gig, in the studio, or even at
home. At its core, the simple footswitch design selects between a pair
of jacks on the left side of the unit. Hook one up and youll
instantly be switching between amps, quickly swapping guitars between
songs, using it to isolate your tuner from your signal, killing your
stage sound as a mute, and more. And with its adorably tiny footprint,
the Mini A/B will fit on even the most cramped pedalboards.