It is designed to allow lighting and sound operators to be able to see the performance, without being in the auditorium itself. This means that they are free to talk to their colleagues in the booth, and also the stage management team and other crew members via the communications headset.
This arrangement enables lighting and sound technicians to monitor the show from a separate location, allowing them to chat with their colleagues in the control room and stay connected with the stage management team and other crew members through a communication system.