I haven't had a need to do this, but is there any reason for a spindle to run in reverse..apart from threading a hole.  I ask because I have a controller that will allow me to reverse the spindle..any advice would be great.  Anyone that can give me advice on weather or not to disable this function....I can program it to not allow reserve spindle speed, but looking for advice before I do it. Its very hard to change the disable function after I impliment it.

What kind of machine ?
Depending on the type of machine, a conventional knee type mill needs the motor to run in reverse for the spindle to run forward when in back gear.

With a large industrial router, we frequently use left handed bits to prevent chipping.