Stan, there are a couple reasons off the top of my head for left-handed bits. Most used are smaller ones for drilling out broken off bolts. As the drill works, it heats up the bolt, and as the bit drills through the bottom, it will actually back the broken piece out. The other use is for gang drills, as every other quill turns backward to the next; ie, cw-ccw-cw-ccw as the gears mesh.
Bob
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