It's for the control of the volume if your Beomaster is in option 0 and the video in option 2.
Pin 4 (speaker on) and pin 7 (datalink) of the Powerlink are used.
It will switch on the speakers when you switch on your Beomaster with a button on the Beomaster and not with the remote.
And you will be able to control the volume and mute the speakers if your beomaster has a volume control and/or a mute button