This video shows more dramatic usage of the Undo Brush and actually shows a number of in-progress images that make great pictures on their own.

This tutorial shows the power of the undo brush when you understand it and can use it as an integral editing item in your "back pocket", because you don't have to think about what you're going to do -- you can just expirement and get inspired, and then use the Undo Brush to take what worked and leave behind what didn't.

This tutorial also shows how to do multiple functions and then go back to the starting image (in the history buffer) and use the Undo Brush on the image quite a few steps back in your editing.

As mentioned, I think it makes more sense to watch this one first, then watch steps 1 and 2.  Then watching this one again will show how the Undo Brush is at once simple and very powerful.