= new reply since forum marked as read
LOL. OMG. LMAFO. IMHO.
plus 
and many others... all predate widespread acceptance of the internet.
They go back to the late sixties and early seventies... and dial in time shared mainframes of that era.
Why did we use them? Because many of us had only Teletype-33
and you really wanted to keep the typing to a minimum. They were noisy and slow.
In addition, we had 110 or (if you were lucky) 300 baud modems to use (that bits per second)...
If you use Linux (based on Unix), this is the reason that sooo many commands are just a few characters long (like ed, awk, sed, cat, cp, tar, etc, etc).
In those days we used a utility called talk to send messages to each other online (all connected to the same computer). So brevity was a key aspect of commuication. Slack (and twitter) are more modern versions of talk.
