You're kidding, right? Turning off CSS is used together with turning of CSS and images to
improve the legibility of some websites.
For example, using Medium with everything on is a pain. But if you switch off JS, CSS and images, very often the whole text of an article fills in one screen, is quite clean and really fast. Using Medium in this way actually becomes a pleasure (unless the images are a apart of the article) - you can navigate the website rarely using the mouse. In any case, I'm not alone in using the web in this way - turning everything on is just a waste of time and resources.
You can check it easily yourself with an extension like disable-HTML that allows turning off these thing instantly.