As long as your tether is fixed, and provides a good firm and strong launch point, I can't see any real advantage with someone holding the chicken loop. What happens if it powers up, or a line snaps or gets tangled round a pulley
Personally, if I didn't have a fixed tether or the ballast to fill a kite bag sufficiently, I would buddy launch holding the kite, and as somebody else mentioned, you get the other person to hand the kite to you, when you are ready, no need to pick it up yourself.
Also, I usually bring the kite very low, depowered and on the edge of the window, basically in the launch position, and I watch my kite, not my buddy's kite. It's up to him to get in the right position for launching .. when it's ready, you get the nod and you let go.
The only time I can think of it being an advantage, is if the other person is uncomfortable holding onto the leading edge, but then if that's the case, you would do it the other way round wouldn't you??