it is essentialy delayed name lock
allowes you to namelock your oponent and tele on top of them when they are offscreen. the way to do it is namelock them with unsumon, then while holding doun the button switch to tele , result is you will end up on top of your oponent. I think you can lose the nl if they go more than 2 (hope not wrong here) screens away
At the OP; it's just for a surprise, usually on WW barbs and Hurri druids who need to be near someone to do damage. You can also unsummon lock someone when they leave town to get their body, and when they say 'Go' after they're clothed, teleport directly onto them from screens off or lay a volcano down before they get to move.