zener diode and EMF/emp

I know the common practice is to use a capacitor in a switching circuit clean up the signal and control emf noise, I am just curious If a zener diode would have a similar effect. does anyone use them in there switching circuits, I know relays use diodes to shunt the coil. other than that is there any practical reason to use them, I have not used them in any of my circuits, and am wondering If I should be using them? I only used a regular diode on the main input in case I am stupid enough to hook up backwards. Thoughts?

zeners are very simple to use. get few and play...

main use of capacitors in power supplies is to reduce ripple. technically using zener could be used to accomplish similar task if the voltage does not drop below zener voltage. however, this would mean that excess voltage is wasted on series resistor. capacitors (and inductors) are storage elements. no (or very little) energy is lost here. another issue is that resistor would act as dramatical increase of "internal resistance" of supply. this is (extremely) undesirable for power supply.