not really: http://i.imgur.com/uxqERat.png (you have to be very careful about what indentation level you're at, how long your lines are, etc, etc, things that people just don't do most of the time)
It's also customary when quoting large sections of text. I'm not sure if this carried over from email, or from academic texts (where if your quote is more than a line or two, it needs to be formatted differently).
