You can use this technique to photograph fireworks, for example. Set your shutter to "Bulb" mode,and cover your lens between bursts. In the result, you have multiple bursts in one picture. But, I wouldn´t use a cloth, because you don´t want to touch your camera, to avoid blur. In film days, this technique was the only possibility to bring multiple exposures on one picture. Today, I would take multiple exposures, and blend them together in post.