Without oxygen, the body will cease to function. Oxygen is a vital part of muscle function and brain function. When you damage your lungs, and limit the amount of oxygen your body receives, everything is affected in a bad way.
Well for one thing we'd die without it, just like how Aux Arcs said. If we don't make sure we're clean and healthy, we can potentially get sick or worse...DIE
Our respiratory system is a marvelous gift! If we do not take of it, many things may go wrong with the lungs, especially when one's resistance is low. To name just a few disorders, there are asthma, bronchitis, emphysema, lung cancer, pulmonary edema, pleurisy, pneumonia, tuberculosis, and a number of bacterial, viral, and fungal infections. But these disorders are not the result of faulty or inadequate design of the lungs. Millions today suffer from lung cancer, bronchitis, and emphysema because of tobacco smoking and other self-inflicted abuses of the respiratory system. How vital it is to take good care of our respiratory system to the best of our ability!