If you work in an office, if you are a dentist, or even a student, being in a position with rounded shoulders for the majority of the day can often lead to shoulder and back pain. You can't necessarily change your job but you can reverse the posture that could cause further issues. These issues can manifest themselves in the gym, especially during weight training. Imagine having rounded shoulders and then trying to press a weight directly above your head. Most people do this. If your shoulders are rounded and you try to force them up (with a weight) then this could lead to a whole host of problems due to poor alignment.
If you struggle with poor posture, tight shoulders or a specific injury in this area, try the above for 15 mintues a night. Put on some therapuetic music and it's actually a good way to unwind!