It allows damp wood to be used to start a fire when dry tinder is hard to find.
[1] Feather sticks are made from dead "standing" wood, such as a branch that has broken from a tree and died, but has not yet fallen to the ground.
[2] The bark and the outer layer of wood are removed to reveal the drier heartwood.
While the flakes can be fairly coarse, the finer they are shaved the more easily they ignite.
[1] This is then blown onto until the curls catch fire: the whole feather stick is then placed into the waiting kindling to start the campfire.