High power zeners are typically used as either a shunt regulator or as overvoltage protection. You would use the above 50W zener to regulate a voltage rail where you need high current but have a supply that needs a minimum load to operate. They would be used with the output of say a solar panel to limit the voltage output, or with a thermoelectric generator so that you do not exceed the voltage rating of the supply or the load.
Often used in older power supplies to clamp overvoltage so that the built in resistance of the supply ( pass transistor with a series resistor so if the transistor goes short circuit the zener is still within limits) will limit current so the load will not have a hgh voltage even if the PSU fails shorted.
Typical in aviation as clamps on power rails, from 400Hz transformers with linear supplies, as a failed supply ( typically a shorted pass element) will not fail the equipment totally, but it will still operate with possibly a thermal warning or a supply monitor showing overvoltage just out of limits, to tell you it is in a failing condition. Still runs but will flag a "change me on the ground" warning instead of stopping a critical system in mid flight, which typically means the landing will be very unplanned and lacking in control.