If I see an em-dash in a comment I stop reading and I've seriously considered setting up a filter across multiple sites to remove any comments containing one.
I know there are legitimate usecases for the em-dash, but a few paragraphs (at most) of text in an HN/Reddit comment? Into the trash it goes.
Not so long ago, they were just a ~75%-odds tell that the user was typing on a Mac.
trying to remember what is the grammatical purpose of it when writing
trying to remember last time I used it