Probably already answered somewhere, but I've tried looking and I can't find anything on it, probably a stupid question as well > >

I went to replace the head unit, disconnected everything from the back of the stock one, and noticed this cord, my new head unit does not have that port on the back of it?
http://puu.sh/8Tnqi.jpg
What does that cord even do? Do I just leave it hanging behind the head unit and it's not needed for new ones?
Is that the cord they use to use to make the dash controls work? because I have the modifry dci jack plugged into the back on my new one, if that does the same thing as the white one, if so does the white one just sit loosely behind the head unit when I put it back in?

Sorry for the noob questions/if they've been answered somewhere else Q___Q just very stuck and confused.

EDIT: Got it installed, worked without it so guess I dont need it :L Not sure how to delete post, but yeah, solved (:

 

it's wiring for the optional trunk-mounted CD changer and/or XM radio tuner