For 3D VR videos, this would be useful for adjusting IPD for every person, rather than use the static IPD of the camera setup. Also, allowing just a little bit of head movement would really increase the immersiveness. I don't need to travel long distances inside the video. If the video is already filmed with static stereo setup, it would be even easier to reconstruct an accurate 4D video limited to short travel distances without glaring errors.