Beyond preventing screenshots, it blacks out the window content in the task switcher, which is useful if someone is looking over your shoulder. This, by the way, is a good way to check if screenshots are allowed. If the window appears black in the task switcher, screenshots won't work.
The idea is similar to the "**" password fields.
Password fields are inputs. Screens are bi-directional.
includes the ability from a user to take screenshots programmatically in case of need. You do not want third parties to be able to; you want the User (yourself) to be able to.
Very impressive.