I am still left guessing as to what this adjustment is for. I dug into it a bit more in the Buildbotics manual and it appears that it is used significantly when a machine has limit switches for homing. In our case, sans switches, perhaps it is simply a layer of protection to keep from slamming into a hard stop.
Meanwhile I am going to leave my Journeyman at the 1.5mm since that was accounted for in the cutting width of the machine. With the 1.5 mm backoff, the machine still has a full 48" of capacity (i.e. plywood width).