Sociologically it's perhaps interesting. One might want to "follow the rules" in order to minimize friction with an intended audience. Also, I'm sure we've all encountered cases where punctuation changes how we interpret a sentence. Then there's the more artistic concern of stylistic consistency. These punctuation "rules" might be better seen as some sort of a protocol standard. I'm pretty sure there are, in fact, several competing standards. Following whatever standard is clearly a choice, but that choice does something for setting up reader expectations.