"Peter Campbell Smith" wrote

I was involved in specifying the video transmission system for the Central
Line, and the rationale given at the time was that they wanted (or maybe
were required) to allow the driver to see the images after moving off.

This RAIB report explains why.
http://www.raib.gov.uk/cms_resources...g_Broadway.pdf
In this case, the train operator was apparently too concerned about checking
signal aspects (he'd been involved in a previous SPAD) that he didn't notice
in the monitor that the passenger was being dragged along the platform.

Peter