Someone must have looked through the triggers actions and come across the 'Set next Scenario' action..

1: What does this do Exactly?
2: I'm assuming its only Single player mode
3: Was there any use for it found other than for the stated above?

In single player, use of this action will make the selected map run without having to return to the menu and select the next map. It's how blizzard linked their campaign maps together. It serves no other function. It does nothing in multiplayer.

Thanks mate! that puts my suspicion at ease.