You might use this technique for many different functions, beyond simple games such as this. For example, you might use these functions for image galleries or navigation. For example, you might have a bunch of draggable thumbnail images. The user can click and drag the file to a certain area, after which something happens. A web page or file might open, a movie might play, or a full-size image might display.
In this example, when the user drags the thumbnail over to a specified symbol, that thumbnail displays a full image.