The position and coordinated movement of the scapula is important. When looking at the upper quadrant it is important to note where the scapula sits in space in relation to the spine, to the other scapula, to the neck and whether it is tipped forward or downward.
Typical instructions of how to "set the scapula" is to bring it back and down. Often what I end up seeing when I cue this way is a depression and retraction of the scap. People are protracted with poor postures when sitting at the computer or looking at their phones so the retraction is good, but often overdone for a resting/starting position. The "down" cue often creates an over recruitment of the lats to depress the scap. The lats also create a downward rotation of the scap bringing the tip of the shoulder down toward the head of the humerus.
There are important structure in that space between the scapula and humerus (also called the glenohumeral joint) including the biceps tendon, rotator cuff tendon and bursa that cushion the joint.
When you set the shoulder back in the way described above you are essentially compressing those structures which can cause micro trauma that can lead to chronic inflammation and eventual tearing of the tendons.
Further, that position pulls on the brachial plexus and vessels coming from the neck to supply the shoulder (not a problem if your posture is perfect the rest of the day but considering most people are slouched there is a low grade traction of the neurovascular bundle happening all day). What does that mean?
Decreased blood flow and nerve input to the muscles of the neck shoulder and arm, increased strain of the muscles by having to work in a lengthened position and in a narrower joint space and eventual injury to the shoulder in the form of weakness, tearing, muscle inhibition, and pain.
What can we do to correct this?
While the cuing of "back and down" is better than nothing as most people are sitting forward. I like cuing the person to think about hanging the shoulder blade on a hook - it allows for a posterior tipping, upward rotation and slight retraction of the scapula. This should be the resting and starting position of the scapula.
All you office workers out there - start practicing - this can prevent a lot of unnecessary carpal tunnel syndrome, thoracic outlet, neck pain, shoulder pain, tension headaches and then some.