Smoking is very bad for your health, and especially after your dentist has removed a tooth. Ideally, if you need to smoke, you must wait 48 to 72 hours after the surgery. If someone tells you to wait only 4 hours, do it at your own risk!
The reason you must wait is that smoking can slow down the healing process in your mouth, and even cause serious complications. The smoke has chemical toxins that not only harm your lungs but also your surgery site. Also, the suction done when smoking can dislodge the blood cloth from the socket it is in.
One major complication is called dry socket. It is a very painful condition around the tooth extraction site, which can cause bad smell and limit how big your open your mouth. It usually happens 3-4 days after the surgery. If you do nothing, it will eventually go away, but if you see a dentist, he can put a desensitizing drug to make it go faster.