It is easy to imagine a simple rampart that would fall apart under the pressure of combat. this system is completely the opposite of simple and can be hardened up by throwing spoil in among the posts. This system would be difficult to breech without effective counter measures. Posts sticking in your chest can easily make ladder work impossible.
It can also be quickly torn down and repositioned easily even at a fair distance. a twelve foot balk is easily carried a couple of miles. Add in the the platform itself is a robust twelve feet wide, the defenders have ample room and flexibility.
I do not think that this construction was actually meant to be temporary either. Wood would need to be cut and prepped. Of course this also clears the surround as well.