Wig snatchin' innit! You can do so much using CSS and HTML. I'd even go as far as to consider it a form of self expression! I have always had trouble expressing myself using words, so this is a great for expressing who I am as a person. Besides, it's fun! It could be useful at one point. I don't know what kind of situation would require you to know HTML (and CSS), maybe for making a website to attract a specific audience or something, for a reason you're not willing to disclose? I don't know. This is also kinda relaxing so that's a plus.
