Well, it all depends upon which way you look at it. Your friend may think keeping weight down is preferable to giving up smoking but I'd sooner find a better way (like cutting carbs) to shift the weight.
Having handled a real lung, blackened by smoking, in a science lesson at school, it put me off smoking for life.
Personally, I can't think of one good reason to smoke, so i hope you have some luck persuading your friend to give it up.