All of the examples are basically differently-styled variations of "clicking on X adds/removes class Y on element Z". Is this all it can do? Would have liked to see some slightly more varied use cases.
I guess if you only need support for adding/removing/toggling classes, and you have no plans of using jQuery, this could be useful. It's 1kb of Javascript, compared to jQuery, which is over 80kb minified. Now, everyone and their dog likely has jQuery cached from a CDN, but it's a good way to reduce unnecessary bloat. If they added one or two common features from jQuery, and used a normal syntax instead of this written non-sense, I could see some people using it as a light version of jQuery.