all of the other inputs are connected to the output, so i would just turn on whichever console i wanted to play and it would be displayed
however a small voltage travels down the yellow video line, because they are all connected there is a small possibility that this voltage could travel up to another console, this may not cause any damage at all but id rather not take the risk, so i have a switch connected to the video line of the first 7 inputs, with the switch OFF nothing gets out or in, and with it ON that particular console would display.
i have some rare/expensive consoles that id rather not risk anything happening to, so they are connected first, everything else is common and easily replaceable, so i wouldnt cry too much if they got fried!