I had Tuberculosis of the lung a few years back brought on by a stressful breakup I went through and when I was at home for 3 months my nurse actually told me that smoking pot would be beneficial to my recovery. I was told that once the golfball-sized hole that was eaten away in the upper meaty portion of my lung healed, it would scar and my lung capacity would be diminished. However, my lung capacity and general stamina has never been better. Never. I had asthma and got pneumonia often as a kid too and even that has gone.
I'm not so sure there is any tar from cannabis but there definitely is resin which is just a concentration of thc. I cannot see how getting a nice coat of that on my lungs is a bad thing.
"We are not human beings having a spiritual experience; we are spiritual beings having a human experience"—Pierre Teilhard de Chardin