That is an old concept I saw it in the early 80s at Playa De Las Americas in Tenneriffe.
In a bar they had six Technics 1210’s and two DJ’s playing.
It is called back to back when two DJ’s play together.
The thing is that they can compliment each other and play some tunes each
It is no need IMO but a cool thing to look at and also I do think they can trigger each other
to do cool stuff.
A friend of mine who usualy is a VJ playing on Pio VDJ sometimes does this with another rather known DJ
called Alex Moreno. I have watched them a couple of times and I do think it is a good way of doing something different
in a club like an event. The same guy also sometimes DJ/VJs together with a very good saxophone player.
That I have not witnessed myself but it is always sold out on those occations.