I recently had a buddy over and he brought his APA that he hadn't shot in a couple years due to a shoulder injury. He drew the bow and looked like a backwards banana and the string was 1 inch past his nose. We lowered his draw length by 2 inch and low and behold he was standing straight and drawing the bow with ease. When your DL is too long (especially 2 inches) your shoulder has lost alot of it's pulling power before you hit the valley. If this happens then that is when you risk tearing something in your shoulder due to the heavy weight and your shoulder at a weird angle.
https://www.youtube.com/watch?v=oG0nb01SGMA
This a great video on the importance of a proper DL