It protects the back of the bow, somewhat, from use and accidental dings that could raise a splinter, especially on softer wood, or wood with very fine rings. But it's not meant as a substitute for bad grain, ring, or knot violations. It's not good at stopping failures due to such things, though it might keep the bow from completely blowing up and hurting you. Generally it's not needed on good bow wood, well designed, constructed, and tillered. But sometimes it does look cool 😎
