Besides spoiler tags, check out any of the sports subs: r/cfb, r/NFL, r/NBA have team flair, schedules, and scoreboards. Without those and the inline images, those communities would lose a lot of their fun.

Spoiler tags is something that really should get a nonCSS solution though, as they work really crappy on mobile.

r/soccer would most probably become half-dead over-night if the team flairs were to disappear. Almost each and every time when I'm reading a comment on there I first look at the flair of the redditor who had made the comment, so that I know who am I answering to. Sports-related discussions are a lot more heated and personal compared to what usually happens on sites like HN or how r/programming was at the beginning. I've actually seen grown people cry with real tears because of a football match, I'm yet to see a programmer cry because some other programmer has used spaces instead of tabs or vice-versa.

CSS adds tons of value in sports subreddits. It's used to display stuff like the league standings and details on the day's game.

....So turn it off?

Reddit has a setting to disable custom CSS on subreddits, so it doesn't make sense why you'd force the subreddits not to have it.

I did disable sitewise around a year ago, but occasionally get reminded when browsing in incognito.

r/rust used CSS on April Fool's day to add overenthusiastic Rust Evangelism Strike Force-type exclamations to the end of everyone's posts. That was pretty funny. FEARLESS CONCURRENCY!

Lots of meme subs hold a lot of their value in their CSS.