I hadn't read about it before. From what I can see now, it looks like quite a neat trick, but I can't really think of many use cases (or, for that matter, real-life situations where this effect is used but reached in another way).

I guess the most obvious use would be for image-based nav where you have on and off (and possibly a separate mouseover) state. Doing this, you would save the overhead of a heap of HTTP requests, which should in theory speed up download times.