It comes down to what is most important to you. If you're talking about smoking cigs, you should stop if you want a better chance at living a longer healthier life. If you're talking about pot, it's a question of health and moreso productivity. Weed makes most people just sit around and not do much. If you're cool with that, then smoke away. You will only quit if you want to. Figure out if you objectively should quit (e.g. because you're smoking cigs and also want to live longer and healthier) then get to work on actually quitting if that's what you decide is best for you.