On reddit, people use it to pretend to "win" arguments by appearing to get the last word (post a reply then immediately block).
So many argumentative and divisive people who seem to get the last word all the time. Now I know what I'm looking at. They just answer and block. Makes me think even less of them.
Or was last I used it. Maybe that has changed.
Edit parent comment to indicate the block. Add it to a few for bonus points.
Rage blocking. Is deffo a thing!
However if it can't be disproven and you actually convince some people, it will be flagged. And maybe even some people stalk your account and bait you into getting frustrated and then getting your account nuked.
This is why 4chan etc are more intellectually honest imo as you can't nearly as easily censor or rule ban someone who makes a vile but persuasive argument.