When I use bench power supply such as below:

[![enter image description here](https://i.stack.imgur.com/0fWo1.png)](https://i.stack.imgur.com/0fWo1.png)

I use the red terminals as (+) and black terminals as (-) and also as ground. But the green terminal I never use and it is connected to mains earth ground.

The PSU as a whole is already earth grounded from its 3-prong AC plug. I couldn't figure out a use case for the green terminal. Why/when would one want to use the earth ground as his circuit ground? A few examples would help.