If you were not perfect enough while taking a photograph of a texture for whatever use, you can easily fix it, align the angle of view, flatten out the perspective and, of course, make it seamless.

If you have a photograph on an angle of a building's wall, say, you can very easily transform the image as if you were looking at the wall directly.

It is a lot of fun and VERY easy to make ridiculously malformed faces of yourself or your friends from photographs.