The positional tracking is useful even if you don't walk around though. Imagine you lean to the side in your chair but you view doesn't change at all - how weird would that be? Or you're stood on the edge of a building, and try to lean over to see below, but you can't because your viewpoint doesn't change. Positional tracking means that would work as expected - it's good even for seated experiences (where a cable isn't really a problem). Besides from what I hear, users get used to the cable after a while, even though all recognize that it's not ideal.