Howdy The sanding block is a grinding stone, it abrades the edge to remove sharp weak edges and create a stronger edge to work. A thin sharp edge will just kind of shatter out of the way with very little force. The abrader removes small amounts of material along the edge, which strengthens the edge causing it to require more force to detach a flake. It can also create micro scratches along the working edge that allows the flaking tool to get a grip, so to speak.
