Image Stabilization is also known as Vibration Reduction in a Nikon and Steady Shot in a Sony. The purpose of image stabilization is to counteract your natural hand motion. In doing so, it helps us to stabilize our camera and hence give us a sharper image. This means that in low light you will be able to use a longer shutter speed without resorting to a tripod.
However, when you camera is on a steady surface or tripod, you must turn off image stabilization because if your camera does not find motion, it will create it.