Today there was a good example of a much needed stretch for a teenage boy I have been coaching in juggling. During the warm-up, we found that the right side of the back of his neck was more stiff than the left side. This wasn't much of a surprise, since he is right-handed and uses his right arm heavily when playing tennis or when using his computer. The neck and upper shoulder muscles would have stiffened over time.
So we got him to stretch out that part of his neck and the tightness he felt there was reduced within seconds. Of course, it would take some weeks of regular sessions of stretching before the muscles become more supple.