The number one answer to this question, for most people, has got to be the control you regain. As a smoker you are constantly being forced to feed your habit. You are constantly being forced to pay for cigarettes, to smoke at certain times and adhere to your smoking rituals. I say forced because this happens even when you don’t want it to.
When you stop smoking, tasks seem to get completed much faster. You spend less money, partly because you are saving money through not buying cigarettes and partly because you don’t go to the shop as often. In other words your productivity increases. However it is the sense of control that most people enjoy the most.
When someone stops smoking, it is a huge victory for them over the smoking habit. It is a huge victory over the cigarette companies. But most of all, it is a huge confidence boost for people when they stop smoking.