In small dosages, it won't hurt you but it certainly isn't doing any good. I would try to smoke as little as possible.
Nicotine adversely affects EVERY major system in the human body. As it builds up from regular use, it can lead to weakened immune function, fatigue, decreased healing time, and long-term diseases including cancer. In fact, nicotine prevents the body from properly disposing of damaged cells, thereby allowing cancer cells to develop.
Not only that, smoking cigarettes leads to a build up of tar and pollutants in your lungs which will negatively impact endurance and breathing.