People on Reddit are scared of downvotes affecting their karma score, so they have to tag controversial comments to make it absolutely clear if their comment is sarcasm.
I have used it because my sarcastic comment, read at face value, might encourage someone to support something I despise. I’m not interested in creating or bolstering that shit, I just want to make fun of it. Karma points never had anything to do with it. I had millions but what’s a million nothings, still nothing. Reddit Karma is just multiplying by zero.
Personally I used it to keep shinigami eyes users from tagging my then-universal handle as problematic when I made an off-color joke. I’ve been banned from subreddits I never heard of because of something I said as a joke in a totally different subreddit