You are often sent out side to smoke
Face unfair discrimination from many quarters
Inferior tobacco is often laced with undesirable chemicals
Efficiency drops if you are denied nicotine
Can make some people sicker than they are, or cause irritation to a condition already present
Can shorten your life by a few days, as you cannot smoke in some nursing homes. But a long unproductive life, is never a good one - you just become part of a medical experiment
Difficult to smoke in the shower, or in the surf, or riding a motor bike
There are other minor disadvantages that come under the realm of, ... "It doesn't really matter anyway".