Isn't the content of the message the only important thing?

Content is multi-level. A chunk of text often means more than the literal reading of the words.

People use forums for many things. Sometimes it's to inform, sometimes it's to set out a position, sometimes it's to vent and bitch, sometimes it's to just wave a dick around, sometimes it's to play social games, etc. It helps to figure out quickly to which category a message belongs and the style or tone of the message (here: nice or mean) is important. Think of it as a fuzzy tag, an email header line, a hint at how this message should be interpreted.

It's not simple, of course, and there is a lot of misdirection and false flags and signaling and counter signaling... basically, it's humans communicating :-)