That would just be artistic preference with the Cobble Face Flatness Depressions layer for a chiseled concave faced brick. I did this cause it already had a concave arris to compliment it's deep verdiept grout and I hadn't seen it done often, in fact they usually do convex (outward) faces.
I figured for the construction of a road, this would prevent wagon wheels from slipping into the grout grooves (especially in the event of separation/fractures) which would wear the wheels. Just thinking constructively.