This was touted as making the cutter less likely to loosen when the depth was adjusted; the lever cap wouldn't be apt to move along its length as much.
Perhaps someone in the viewing audience can toss one on the bathroom scale and get back to me in avoirdupois weights, not metric, please.
Similar holes can be found along the sides of the planes so that they could accept one of the many fences ones that can be adjusted to bevel an edge that were offered over the years.