The benefits of a classless approach to CSS
I first experienced the web in the mid-nineties. At that time CSS wasn't really around and even if the first browsers supported it, many pages were just text-heavy unstyled documents. Today you would consider such an approach as luddite, yet since the H in HTML stands for hypertext you could argue that keeping styling concerns out of markup is the purest form of authoring a document for the web.
Today's default choices are quite distinguishably different from that. A minified version of Bootstrap 4 ships 117kB. As a comparison: I would have to write about 60 to 80 additional articles on this site to match that weight with an equal portion of content. And while at it, I'd have to clutter my markup with classes over classes. There are of course slimmer css frameworks than Bootstrap, but nonetheless, my main motivation is in the writing down useful things, therefore I decided to approach the styling of this site quite radically with classless CSS. All styling decisions are taken by CSS which is targeted by element selectors only. If I'd bother to minify it, that would clock in little over half a kilobyte, and even unminified it is less than 1% of bootstrap.
But page weight isn't the most important thing. A classless CSS approach enables me to author content without intermediate representations (e.g. the Markdown flavour du jour in combination with a static site generator) directly in HTML while still allowing me to focus on the content.