Brian Gaff formulated the question :
However the current drain of modern lights is one heck of a lot less than a
bulb and arguably, less likely to fail without the driver being alerted via a
snazzy dasboard icon.

More than just snazzy, the system can be very practical, very useful. I
can plug the caravan in and know all the car and all the caravan's road
lighting is functioning. If there were a failure on route, I would know
immediately and know precisely which lamp had failed.

They don't even have to completely fail, a poor connection or
flickering lamp is enough to trigger a fault condition.