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The rift has cameras that track your movement. That is the main difference that you are looking for. I've used the rift dk1 with extension cables and can actually move around quite freely, though obviously not as much as a wireless setup. With gearvr you can move around but the headset/game doesn't actually know you are moving around as there is no external tracker or reference point like with the rift.

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.

The GearVR doesn't do positional tracking at all, just basic head tracking. It also has to use your smartphone GPU, which means games are severely limited in comparison to a Rift connected to a GTX 970 or 980.