exercises that place the arm above the head become difficult if not impossible after some shoulder surgeries. these exercises position the shoulder in a comfortable locked in position. training in this position (eg. pull-ups) serves to strengthen muscles like the lats, which in turn support the shoulder in its resting position. i cant say avoiding surgery is fool proof - there is a markedly higher risk of dislocating, and many exercises (eg. bench press) become impossible with a loose shoulder joint. but personally i dont care, my destroyed shoulder becomes fixed after consistent pull-up training, do not see a need to lose half a year in recovery atm.