This is optional, plasma cutters don't have to have a Z limit switch. But it allows us to home the machine to a known safe position out of the way and it allows us to set soft limits to enforce a safe zone of travel, and it allows us to have a global safe Z height in machine coordinates. We can also use that limit switch circuit for a break-away torch holder stop switch when the time comes. Since we only have home limits on one end of each axis, we rely on soft limits to keep the machine from exceeding the other end of travel, and it certainly doesn't hurt to have that on the Z axis. I just mounted a normally closed micro lever switch below the lead screw so it strikes the nut (or the screw post) at max height.