A patch bay can be set up to run different chains depending on where you plug in. For instance, the patch bay could be wired to run through pedal A, B, C, but if you plug in at another point it bypasses A and starts the chain with B.
It is used mostly as a junction box, but there are some interesting tricks you can do with a patch bay. So in my case I could have it set up to run 4cm with amp or just direct to amp depending on where I plug the guitar into the patch bay.
Unit in question is Hosa MHB-350.