Outer sleeve on upper control arm bushings

[MaximRecoil]

1969 Dodge Charger, 318, automatic

What is the purpose of the steel outer sleeve that slides over one of the bushings (the one that is toward the back of the car) in each upper control arm? If it is important, why don't both bushings in each upper control arm have it? One of my upper control arms doesn't have the sleeve installed over its rear bushing. Is that something to be concerned about; i.e., is it worth tearing it apart to put it on there?

[b5blue]

It's a HD part, B Body Police and Taxi Cab service reinforcement bushing for severe service. Most likely to prevent the A arm bushing sleeve from cracking on cars that saw 100,000 miles of hard driving (Hitting potholes and curbs ect.) per year. Placement on just the rear as it sees the greatest forces (Like hitting a pothole.) moving forward at speed.  I thought about adding them back when I used my car more like a truck working construction. As my originals were fine when rebuilt and I have a set of new reproduction A arms to install (After I install "offset bushings".) I decided it just not needed.