The rollover joke for this XKCD cartoon says
If used with software that could keep up, a scroll wheel mapped to send a stream of ’undo’ and ’redo’ events could be kind of cool.
So of course an Emacs geek, ncsuwolf, immediately implemented it. It’s probably not something you’d really want but it is neat that it was so easy to do.
In the comments, someone else suggested using the scroll wheel to control the Git time machine. That might be slightly more useful but others really liked controlling undo/redo with the scroll wheel. If you’d like to try either one, they’re each only 3 lines in your init.el.