Over-travels that used to crash the probe into your part instead now bump the halo and alarm the machine, just like it would if the stylus detected an unexpected surface. Hit reset, and carry on with your day. 

This product is sized for Haas/Renishaw OMP-40 series probes, with the Renishaw stylus. 
*Disclaimer*  Obviously the probe has to be "on" for this to work. If you call the probe up as an endmill and try milling a pocket with it, this will not help you.