I smoked 2 packs/day for nearly 20 years. Stopped 11 years ago. I couldn't go back to the stench, filth and chronic low grade ill health that heavy tobacco use produces. Furthermore, I seem in good shape - hey, I might even have gotten away with it.
One unexpected downside. I stopped through Nicotine gum. This is as addictive as hell and I still chew ALL DAY even now. The gum comes in blister packs with sharp edges. Bloody painful when stuffed down Lycra cycling shorts.