Great question, until I took it apart I didn't really understand either. I think it is just simply the suction that is produced inside the chamber that should be channeled out toward where you want to pick things up with the vacuum. If the bag gets too full, or some other obstruction, that suction gets stuck in the chamber and pulls the orange part down against the spring, indicating there is an obstruction, causing the suction power to not be focused where it should.
