The general rule of thumb for capturing sharp, handheld imagery is that you should not handhold a camera at shutter speeds slower than a shutter speed equivalent to the focal length of the lens. This means a 200mm lens shouldn’t be handheld at speeds slower than 1/200-second, a 150mm lens slower than 1/150-second, a 50mm lens slower than 1/50-second, and a 20mm lens slower than 1/20-second.

Steady Shot on Sony came out; with this image stabilization, it was possible to handheld with much longer exposures.

If it is that GREAT! Then why not use it all the time.

Image stabilization on fast-moving objects results in blurrier and shakier photos than without the image stabilization. Furthermore, image stabilisation relies on movement, if you mount your camera on a fixed platform (tripod or similar) you risk creating a self-oscillating back feed loop. Image stabilization also seems to affect the mid-range distance bokeh, because the background in the scene is slightly moving differently than the focus point in the optical path, this resulting in a bokeh that does not have that simple shape and regularity we expect out of the highest quality glass.

Rules of Image Stabilization

1. The first and most important rule of image Stabilization is this: never switch it on unless it is actually needed.
   
2. Image Stabilization should be off if your shutter speed is over 1/500.
3. If your subject is moving, you still need a shutter speed that will stop that movement, not image stabilization.
4. Never use Image Stabilization on a tripod.