If you've followed me for any extended period of time you'll know one of my favorite yet easily butchered exercises are ROWS!!!
One thing that I continue to see is the idea of "STAYING PACKED" as opposed to allowing for free motion of the shoulder blade. The shoulder blade needs to be able to move freely on the rib cage to maintain positioning of the ball in the socket.
See if you keep the shoulder blade packed (squeezed hard down and back) then you create a lot of torque going across the glenohumeral joint. To put it into plain English: the more you stress out that part of your shoulder, the greater the chances you will create some sort of impingement. By not allowing the scapula to move, you create a lat dominant style row (I.E: imbalanced movement).
This is in contrast to proper movement during a row where you're allowing protraction of the scapula and retraction when pulling your arm back. It all comes down to this:
When your arm moves forward, so should your shoulder blade. When your arm moves back , your shoulder blade should move back. This concept applies to pull ups as well.