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 setup enables lighting and sound technicians to view the show from a separate area, permitting them to converse with their coworkers in the control room and also stay in touch with the stage management team and other crew members through a communication device.