Floss are made to remove any debris or "leftovers" in-between your teeth, as well as, massaging your gums. If your gums bleeds lightly, this is normal. But as you floss daily, it will not bleed anymore. Sometimes, brushing is not enough since it cannot get in to remove those "leftovers" so, flossing is the best answer to it.
It reduces the possibility of gum disease, cleans between your teeth and reduces decay and bad breath. Also, there are studies that link not flossing and the resultant plaque with heart and cardiovascular disease. There is really no good reason not to floss.
It's NOT as far as I'm concerned. For years when I'd go to the dentist, he'd say," I see your are flossing, way to go", yet I hadn't flossed for many years. Today its been at least 20 years since I last flossed, but still No bad breath or cavities. Moreover I haven't changed my tooth brush for three years, but I do always brush my teeth after eating. Yet no dental problems. So, so much for the importance of flossing.