[RedLefty]

Your thinking is a little bit backwards here. The shoulder is an inherently instable joint (the only ball and socket we've got in the body that works in such a huge range of motion), so in that sense, yes, you should do some things to keep it as stable as possible through the ROM.

Yet the RC is just a small part of this. The shoulder joint has many muscles that have to work together. Often any dysfunction or weakness is in other muscles, but you end up feeling pain in the RC area due to acromion pressure. But that's not the source of the problem. For example, if you have a really weak infraspinatus and/or teres minor, your scapula may not lay nice and flat and low. It might "wing" out a little, and since all those bones are connected, when the scapula wings out and up, everything else shifts. End result: RC pain. But you'd need to fix the scapular position, not the RC.

Edit: I just realized that umass said pretty much the same thing. Except he said it better and shorter. Dang.