guide player movement to make it possible for other players to set up ambushes in known bottlenecks. Thus increasing pvp posibilities and encourage group play to counter it. Note that some cliffs you can still go up and down if you know the trick, but it is a hassle. Easier to just ride a horse around to the right side. Also there are many hidden ways up and down that are only noticeable by a texture difference in the cliff. thus benefiting people who know the lay of the land over those who are new and just follow the clear cut roads. Play for a while and it will start to stick out.