Haptic Feedback
Lets you know that the video has started when you can't see it.
Haptic feedback is the use of the sense of touch in letting you know something is happening. The vibration tells the story.
In the case of the NuPro it is an on/off selection you can make to vibrate the camera for a few seconds when you turn on the video.
If your camera is in a position where you can't readily see it, such as on your helmet, on the mast of your windsurfer or some place similar it could be possible that you didn't actually turn on the camera when you pushed the button.
With a camera like the GoPro that would let you finish your run with nothing recorded it would be a big disappointment. But with the NuPro you have the choice of haptic feedback and can be sure you are recording.