I had a rotator cuff tear repaired about two weeks ago. My arm is in a bulky sling with a big pad under my armpit. I'm having trouble doing anything with this thing. Is it really necessary?
Studies have shown and confirmed the value of the abduction immobilizer you describe. Putting the arm in slight abduction (the arm is 45 to 60 degrees away from the body) improves blood flow to the rotator cuff. It also reduces any tension on the repair.

This special sling is especially important during the early phases of healing. Most surgeons recommend its use for the first four to six weeks after surgery. You are already one-third to one-half of the way there. If you can hold out another two or three weeks, you will have a better result than if you remove this bulky splint.

You should be able to remove it daily in order to do your exercises. Otherwise, it's strongly advised that you keep it on to avoid overstressing the healing tissue. It should be work full-time at least until the end of the fourth week. Some surgeons suggest wearing it for comfort for the next two weeks before gradually eliminating it.