There are many situations on-set where it would be valuable to be able to communicate to a specific department, but be able to listen to another channel simultaneously. For instance, you have to listen and talk to the camera department, but also need to listen to the AD channel all of the time: through CommsLink you can achieve this on a single headset.
Another example, if you are running a remote production and your director is not in the same geographical location as the splinter unit(s). Through CommsLink these remote units can be on the same radio / comms channels as the main unit and the director can communicate with the splinter unit(s) seamlessly, whilst watching their remote uplink video!