Even if it was fun I often felt it was useless because the skills I was acquiring were only applicable for game development and that was something I was not interested in.
It was quite a shock to me when I found myself working on a WebGL demo for Google² and all what I had learnt in the demoscene paid off (and has continued paying off ever since!³⁴).
At least JS-powered renderers can do something about making sure it looks the same in all browsers. With CSS you can't do anything about the fact that this simple demo doesn't render correctly in Safari/iOS and Firefox/Android.