This is just useless trick in AV. While waiting some to start fight with vanndar u can kite him with this place when u are bored.
Just stand where i stand in the picture and agro him. He will run that red line. Then just jump down when he is near and he will run back the same way. Do this until u die or some1 picks the agro.
Searched with Vanndar and Alterac Valley words but didnt find.