This is what external rotation of the shoulder looks like, with the humerus as the axis of rotation. For weightlifters who can do this it's like getting longer forearms and shoulders with more cushion for the bar. Get good at this and it will save your wrists and clavicles a lot of pain.
Lifters who have trouble racking a front squat on the shoulders usually have tight internal rotators of the humerus. A lifter with tight internal rotators can rack the bar on the shoulders using a cross-arm grip but has trouble with a traditional grip when the hands are wider than the shoulders. This is the best stretch for them.