Home switch = a way to accurately set 0,0,0
Limit switch = a way to keep from overunning the physical limits of your machine
You can have either, both or neither, but for safety sake you should have at least limit switches. - and, of course, an e-stop.
There is no need to have separate switches all wired separately to your BOB. Whether it is a limit or home, Mach does something when a switch is triggered. If it's during the "ref all home" then it moves each axis until a switch is triggered and then moves to the next axis (z, y then x, I think). If it's during normal operations then everything stops when a switch is triggered - doesn't matter which one, it just stops.