They are often used in the back side spindles of screw machines, for drilling the back of parts after they are cut off. I used to have a set of fraction and number lefties. Later, when I got to dealing with graduate students and PhD's they came in handy, just the thing to drive the "smart people" nuts. The time spent regrinding them was worth it.
"I am not academically qualified. I am what I call QBE - thatís my degree - Qualified By Experience."
Rupert Neve, Audio Technology Magazine Issue 1, March 1998