All shoulder dislocations cause some amount of bone damage. In the most common type of dislocation, the head of the humerus (upper arm bone) is forced forward and out of the shoulder socket. This is known as an anterior shoulder dislocation.
Even if the shoulder is reduced (head of the humerus is put back in the socket), the soft tissues around the shoulder have been overstretched. If the humeral head hits the rim of the socket with enough force, there can be damage to both areas (the humeral head and the glenoid rim). This is the type of injury you have referred to as a Hill-Sachs lesion.
Studies show that there is always some amount of bone damage with a first-time anterior dislocation. If the defect is moderate-to-severe, the loss of bone results in abnormal shoulder motion (biomechanics). Many patients develop recurrent shoulder instability meaning the shoulder dislocates over and over.
Experts in this area say it may not be enough to repair the torn or damaged soft tissues (tendons and ligaments) if there is also a bony defect. The soft tissue repair or reconstructive surgery is more likely to fail if the bony lesion(s) are not addressed as well.
Anatomic repair (putting everything back the way it was meant to be) is always preferred. But a nonanatomic approach (e.g., using bone grafts, removing the humeral head, shoulder replacement) may be necessary in cases where there is more severe damage. Your surgeon is the best one to advise you. When formulating the best plan of care for you, he or she will take into consideration your age, activity level, severity of injury, and bone quality.
All studies show the same thing: the natural history of Hill-Sachs lesions (i.e., what happens without treatment) is chronic instability. In other words, the shoulder dislocates over and over further stretching the soft tissues and damaging the bone.