Mark Rippetoe and Starting Strength don't advise sticking to light weights for rotator cuff work.
He says that your rotator cuffs will strengthen in the appropriate amount if you just press correctly.
Pressing actually strengthens the rotator cuff muscles.
When you press overhead and finish the lockout correctly, all of the muscles of the shoulder are tight and contracted. As the weight goes up over time, the strength of the finish must increase and the force produced by all the contracting muscles must therefore increase as well.
Since the press uses the rotator cuff muscles isometrically to stabilize the lockout position at the top, and since proper form ensures that they are active in this capacity as well as safe relative to a position of impingement, it seems as though the logical way to strengthen the cuff muscles — even cuff muscles weakened by injury and surgical repair — is to press correctly.
In the correct press lockout, the weaker muscles are supported by the healthy ones, and as the injured muscles heal, they are able to resume an increasing amount of their normal functional load if correct technique is utilized with weights light enough to permit it.
In this way, the injured muscles can be brought back to normal function while performing their normal function, in effect given no choice but to heal by doing what they normally do.
