Similar to the Draw brush, but it always deforms the mesh from the original coordinates and uses the Sharper Falloff by default.
Draw Sharp is useful on high density meshes for creating cloth wrinkles, stylized hair or hard surface edges. To further sharpen or polish sharp edges in the case that the mesh density is not enough, it's recommended to use the Pinch, Crease or Multiplane Scrape brushes.
A limitation is that the brush does not remesh the sculpted surfaces with Dyntopo enabled. Because of that, a better brush to use with Dyntopo can be Crease.
On Subtract by default to carve in creases. More info at Direction