Most people opt to use two I/O ports for controlling a projector screen, one for roll-down, and one for roll-up.
Another option is to connect a PIR motion sensor, which is brilliant for designing eco-friendly installations. You can make the PIR turn off your installation when no motion is detected. Remember to time the system, so that it doesn't turn off when someone is still there sitting very still.
What you could also use your I/O for is a keyboard lock, which prevents unwanted handling of the control panel by locking certain buttons.