Basically, the idea is to see if it's possible to merge the inbox and sent messages together, so that a user could see both sides of their conversations with people.
I was looking through mine (though a few years old) and was noticing how i could only access one side at a time, a lot like older cell phones when they introduced text messaging.
However, with the newer designs for cell phones (and various IMs) users can see both sides of a given conversation.

Idk what the full technology is for the site design and such, but I figured, if it were possible to do this, it would certainly be useful. This way, sure, you could essentially send emails back and forth, but at least you'd know exactly what was going on, both ways.
Unfortunately, due to the lower interaction on this site, i have no idea, if this should even be done right now. >.> Though, I do hope to see it go back up someday soon, but, if it doesn't, i wont be disappointed, if it proves to be that we cant streamline the messages some.