I've been diagnosed with a grade 3 AC joint separation from a mountain-biking accident. I'm 42 and a serious social rock climber. I've had one orthopedic surgeon recommend I have the operation and another recommend against it. What say you, Dr. J?
Do it! The boney lump on top of your shoulder is actually a joint between your collar bone and shoulder blade. More commonly known as the AC joint (acromioclavicular), it is the one joint connecting your arm to your body. And now it is not there. Shit. Get that puppy stitched, stapled, lashed, lassoed and retro-bolted back in place.
The operation can cause some biomechanical issues. For an active person these are far less than the potential problems if the joint is left separated.
If you are inactive and choose not to have the op, you will suffer every now and again over the years, but the most notable problem will be early joint degeneration (osteoarthritis) in and around the shoulder.
If you are a climber and decide against the operation you will likely be in an asylum for pathological frustration within a few years. Don't risk your safety or that of your neighbors - cancel your gun license and hand in your nail clippers. Your shoulder behaving reasonably without an operation is about as likely as Sarah Palin being given an honorary doctorate in feminist theory.