A dull pencil leaves a wide mark, while a sharp one is precise and better contrasting. There are times when a pencil is still better than a marking knife. To keep my pencil "scary sharp" without stepping away from the power tool, I stick a P220 adhesive sanding disk to my tool (pictured here on my bandsaw). On my table saw, I put one in the top channel of my fence where I also leave a pencil. Sandpaper sharpens pencils much better than a mechanical sharpener can.