like the name says, its a safe zone inside of splintertree post. the only reason i would guess you would need it would be if you are alliance. you can just kinda sit up there and shoot at horde (havnt tested that theory yet, but i dont know why it wouldnt work.)
heres a SS of where it is. its very simple to get to.
in order to get there, here is a SS showing how to get up there, although its basicly just running up the tower and jumping off at a point thats higher than the stump.
yeah, i know i shoulda tested weither or not it lets u shoot at horde players, but like i said, theres no way that it should be able to stop you.
WARNING
like i just said in KuRIoS's post about another safe spot, and i actually had this happen here, THE GUARDS MAY OR MAY NOT PORT UP TO YOU! if this happens, i would highly suggest using anything u have to kick the crap out of them, or jump down and run like hell.
Enjoy!