The screen turning off when it automatically locks is an added bonus; the priority is to be able to command the system to simultaneously lock and turn off the screen. You’re correct that the setting at zero seconds safely achieves that.
I’ve had other, more stupid uses for running commands, though I don’t think any are actively in use.
Taking actions on network reconfiguration, charge completion, and SMART failure are all things that spring to mind. It’s nice to be able to set those kinds of things in a GUI rather than putting them in /etc/something.d