Playing vs Non-Playing departments - what's the difference?

Playing vs Non-Playing departments - what's the difference?

OK, so I'm setting up a Nova site for a new sim. As I go poking about the departments and positions, I notice - there's a selector to allow a choice whether a department is playing or non-playing.

On a whole-department basis, what does that even mean? Or what is it supposed to mean? What does it do?