Imagine for instance grass, sand, foliage, smooth surface, simply no edges or orientation points or contrasting spots anywhere in the image. As I said, almost impossible to line up "by eye", tending to errors. In such case using opacity is also useless. My approach with pencil and paper is still much better :-( .
Update:
But you inspired me and I have found this workaround:
Both images to two layers, and because one selection works for both of them, I can do Copy/Paste with changing the active layer, without any use of the Move tool. If I had some keyboard shortcuts for switching active layer, I need not anything else...