It's mainly for Americans who don't have scart connectors. Their equivalent of RGB is "component" and they will wire several component video sources into the amp with one lead going out to the TV.
Most people in UK don't bother using video switching in the amp but wire the sources directly to the TV via scart.
I have been holding a one man campaign against video inputs in AV amps as they degrade the picture and obviously cost something to fit.
Manufacturers like Cyrus and Naim have at last started bringing out AV processors without any video switching for a purer signal but they will sell an add on box for anyone that wants one.
I hope that everyone follows suit but as the major AV market is over the pond, I doubt whether they will.