This exercise is not so much a specific stretch as a movement pattern. Throughout the motions you are affecting muscles of the chest, shoulder, neck, back and hips. The primary emphasis of this routine is to “verticalize” your posture and is a primary correction for slumping/slouching. These patterns are very common in individuals with high sitting requirements like excessive time at a computer or driving.
Interestingly, “rounded shoulders” can cause pain between the shoulder blades but also numbness/tingling of the arms and hands. It is also frequently involved in a “forward head”, which leads to neck pain, headaches, and TMJ or an “anterior pelvis”, which leads to lower back pain – especially right across the beltline. Exercises to correct for compensatory movement are often performed not where it hurts but are for why it hurts.