The relief and relatively narrow blade keeps the tool light and maneuverable. The curve concentrates the cut on a flat surface, which is essential to working freely. The effective curve and tool width can be reduced by angling it, and very fine shavings can be removed -- or huge amounts of wood depending on the pitch held. This is different from a spokeshave, which can only cut at one angle and one set depth. You vary a drawknife's angles continuously as you work. By feel as much as anything else. It's particularly effective to work with knots and difficult grain. You can flip it upside down, and reverse direction, while controlling depth, angles, stroke and strength. You can cut inside curves, unlike planes (other than a compass plane) and much easier than a spokeshave. A drawknife is a virtuoso instrument for working wood compared to fixed shoe tools. Kinda like the difference between a xylophone and a violin.
