Ben Crair, writing for The New Republic:
“In the world of texting and IMing … the default is to end just by stopping, with no punctuation mark at all,” Liberman wrote me. “In that situation, choosing to add a period also adds meaning because the reader(s) need to figure out why you did it. And what they infer, plausibly enough, is something like ‘This is final, this is the end of the discussion or at least the end of what I have to contribute to it.’” […]
Now, however, technology has led us to use written language more like speech—that is, in a real-time, back-and-forth between two or more people. “[P]eople are communicating like they are talking, but encoding that talk in writing,” Clay Shirky recently told Slate. This might help explain the rise of the line break: It allows people to more accurately emulate in writing the rhythm of speech. It has also confronted people with the problem of tone in writing, and they’re trying to solve it with the familiar punctuation marks that the line break largely displaced.
I definitely use the line break in text messages and IMs, but I guess I just don’t communicate often enough with angry people that I’ve noticed the period-means-I’m-angry phenomenon.