I saw this in the recent remake of Arthur (which isn't as bad as I feared, pretty good actually).
3,000 people US people per year loose fingers to saws! Ten per day (not ten fingers, ten people. Probably more fingers).
The machine feels the electric change if a body touches the blade and stops. The reaction time is amazing.
I know I wouldn't let my kids play with a table saw which didn't have this feature. :-)