Does the existence of a NZ serve any useful purpose? Or is it just as good to have my territory come into direct contact with yours?
I think the purpose would be to minimize the squabble over where exactly my space ends and yours begins. If neither of us can enter a certain area, we can't mutually claim systems/planets/resources. You can't very well build a fence in space, not really practical.
There's no bodies of water in outer space, but there is vast emptyness; so its almost like an international waters type thing. Sometimes we heard that there were planets and outposts in the neutral zones, but I think the whole situation was poorly explained, and perhaps done so on purpose merely for plot reasons.