It's harm reduction for me and allows me to still perform at a reasonable cardio level in beer leagues. Now my evidence is shotty, but my lungs "feel" better and I have a noticeable improvement in cardio when I haven't touch a cigarette in a few days and have just been vaping. My ability to stay on the ice (I play hockey) is noticeably better. I don't start getting really tired until the third period, whereas with cigarettes I am dead by the second period.