As a child I was always intrigued when the altar boy lifted the chasuble of the priest during the elevations. Normally two did it but in a very discreet tight way.
Today, however, it is much exaggerated by some. It is simply to keep the chasuble from pulling the alb when the priest offers the high elevations so people can see the Host and Chalice. It need not be exaggerated.
I know that when I celebrate our ad orientem OF Mass each Sunday and no one lifts the chasuble, I can feel it pulling. A simple lift would help immensely! But it need not be overdone, noble simplicity works quite well in this case!
With a raised chasuble to Fr. Z who posted on this with the photos below!
Just right, but two doing it would be better!
Just too exaggerated and too pompous!