- Drill out sheared shafts.
- Drill a shaft to use a T-piece.
- Drill out a damaged thread.
- Cheap ones may bend or fracture.
- Can be sharpened to extend usable life.
Cobalt drills are an excellent compromise. Harder the HSS drills, less brittle than Tungsten Carbide but can still be sharpened to extend their usable life. Expensive but probably worth the investment.