Nope, they're for carrying video signals much like an RCA cable can (in fact the two connectors can be swapped as you like as long as the format is the same.) They're far more resilient connectors though and lock in place - as oppose to the more domestic RCA connectors tend to be designed to be connected a few times in their life and then just left alone.
BNC cables are often daisy chained too, hence the in / out you've got there. Makes it easy to connect more than one display to the same source without running heaps of cables!
As such BNC is far more widely used in the pro video world where things need to a) be reliable and b) stand up to far more abuse than in the home - think tours, theatres etc. It's actually quite unusual to see them on home appliances at all, so just treat it as an added bonus if you should ever need to use it - though that is unlikely!!