Over-voltage protection for microcontroller ADC input pin.
There is no reason not to use this circuit except that it only does half the job - voltages below ground will not be clamped. If you have a low impedance source a dual Schottky diode is fewer parts and less PCB area. 

This circuit (and similar ones) has/have an advantage in that it/they shunt(s) current to ground rather than to the supply rail. The latter situation means that the supply rail could increase in voltage out of regulation, since most regulators will not sink current, possibly causing improper operation or even damage.