The advantage of having keys on the screen is that you have some feedback when pressing them does make something happen. While you can actually feel physical button presses, they don't always come with that assurance. There might be times when you want to have the same vibration feedback on your hardware keys. There might also be times you want them to give an even stronger feedback. For those times, the VibeOnKey app delivers such functionality with minimum fuss and cost on your phone's hardware.