There seems to be a lot of confusion about the rotator cuff and how to train it so this will be part 1 of a two part post on proper rotator cuff training for preventing shoulder injury and improving performance. Today will focus on strength and some time later this week I will address mobility issues. Enjoy
Every joint in the body operates somewhere along a continuum of mobility and stability. Certain joints have limited motion and very high degrees of stability and are therefore more difficult to injure without excessive force or misuse. The knee for example is a very stable joint. It only moves in one plane and requires blunt trauma to cause injury in most cases  The hip is slightly more mobile. Think about how it moves in all different directions, allowing you to perform squats, lunges, running and whatever else you do with your hips. It still has some inherent stability because of the location of the femur in the hip socket.
The shoulder is the least stable joint in the body. Unlike the hip there is very little stability provided by the joint structure, but in exchange we can move the shoulder to extreme ranges not possible in the hips. This is because the femoral head sits just on the surface of the glenoid fossa. Imagine a golf ball sitting on the tee. It's there but as soon as something hits it we could see problems, unless something is holding the ball in place. For this reason stability has to be provided by the muscles and ligaments surrounding the joint rather than the physical structure of the joint itself.
|Ball = humeral head, Tee = glenoid fossa. Analogies are fun!|
At this point it should be evident that in order to decrease our likelihood of injury at the shoulder that we need to strengthen the muscles and ligaments holding the humerus in place. Enter the rotator cuff: This collection of four muscles make up a large portion of the surrounding structure to your glenohumeral joint and if trained properly can provide adequate stability to ensure healthy shoulders.
Look in any anatomy textbook and you will see the actions of each of the muscles:
Infraspinatus and Teres Minor - external rotation
Supraspinatus - abduction
Subscapularis - internal rotation, flexion and abduction 
However there is an extremely important function of all of these muscles that many textbooks will not mention. Every muscle of the rotator cuff provides compression to the joint through varied joint actions and ranges. This compression along with actions from a host of other scapular stabilizers provides shoulder stability. What this means is that we are only training part of the function of our rotator cuff through exercises like these.
In my experience exercises like the one featured above are over-used and over-rated.  I am not saying they do not have a place, simply that they are not a comprehensive rotator cuff training program and are often superfluous if your upper body routine is adequately balanced in the first place. (this is increasingly rare, but upper body programming will be a post for next week)
True rotator cuff function involves the shoulder reacting to load and velocity to protect the glenohumeral joint. The rotator cuff responds well to most compound upper body exercises if performed correctly. This includes deadlifts, rows, chin-ups, pushups, single arm pressing activities and even bicep curls. You can also utilize upper body unstable surface training as an addition to the big bang exercises we just covered. In order to get the most out of all of these exercises with regard to rotator cuff strength and function focus needs to be placed on keeping the shoulder "packed". That means retracted and slightly depressed with a neutral spine position. So for the next week try dropping all of your extra shoulder work (side raises, upright rows etc.) and toss in a few extra sets of the big lifts or maybe some of the following reactive stability drills.
Staggered pushups and bearcrawls
Bottoms up KB press: Advanced rotator cuff training
Sometimes weak stabilizers are what's holding back your progress in the gym and leading to poor posture and even injury. Try taking a new approach to rotator cuff training and let me know how it goes!
 if you are complaining about knee pain unrelated to a traumatic injury it is probably because you've been misusing your body for a very long time
 the larger pectorals and latisimuss dorsi are also responsible for internal rotation, a primary reason that most weightlifters are overly internal rotated
 anecdotes are a dime a dozen in the fitness industry but I haven't done any direct internal or external rotation work in years and my shoulders are as mobile and strong as they have ever been
 i hate these exercises