Listen, if you feel like you need a cig every now and again to relax, that's one thing. But if you're smoking tobacco or marijuana, doing so a few times a day and letting it get in the way of your life financially or otherwise just isn't GTO. With any vice, moderation is key. No harm, no foul if you want to smoke a cig though- many people do much worse to get their buzz, not that it makes smoking cigs healthy.
As for smoking cigarettes and poker, I can't speak on that myself since I'm anti-tobacco (but pro weed hehe), but I'm sure if your body is used to having nicotine in it's system, it requires you smoking to perform at maximum mentality. May be fine short-term, but this dependability long-term is obviously unhealthy.
When I was young, my parents would return home from the casino absolutely reeking of that smoker smell. I'm glad I wasn't around poker and casinos until after smoking regulations were implemented. My dad said you used to not be able to see across most poker rooms due to the smoke. No thanks! I may be pro-weed, but even if it were federally legal to smoke, I wouldn't want it or any kind of smoke at my table (or vapor for that matter). Step outside or hit up the parking garage. You can take a 15 minute break from a cash session, and no one at the table will be upset.