One of the shortcomings I experienced when I tried sawn flints is that they did not "self-knap". Because the edge is perfectly square, they just seemed to round over with use. Knapped flints have an irregular edge which is jagged if you looked at it under a microscope. When the "teeth" hit the frizzen they break off and the chip carries into the body of the flint. New fresh edges are exposed. This way a flint can stay sharp, somewhat, even while becoming shorter. The grain and fracturing qualities of the particular stone used, as well as the angles, will determine how well this works.