When one files off the bolt ledge, the bolt can pop up too far into the cylinder notch and hit the metal with such force that, with time, that bolt can penetrate the metal into a cylinder. I have seen that on a couple older Colts.
That's why it is imperative that one dress the bolt head afterwards to maintain its original protrusion depth. Also, because the bolt head is pivoting in an arc on its way up, the angle at which the bolt head contacts the cylinder is changed slightly when one alters that ledge. So in addition to dressing down bolt head height, the shape must be altered as well with more material being removed from the front of the top of the bolt head than the rear.