Smoking greatly increases the chance that you will develop vocal nodes, and that the quality of your voice will be permanently changed.
After years of singing, many singers, even those who do not smoke, suffer from permanent, tiny lesions or scar tissue that grow on the vocal cords. These are called vocal nodes, and they make the voice sound rough and weak. They also make singing or speaking painful, and at their worst, they may cause one to lose one's ability to speak or sing altogether for a time. Vocal nodes are the result of wearing out the vocal cords through prolonged straining of the voice by shouting or singing with poor technique. Large vocal nodes require surgery to remove, and vocal rehabilitative therapy for the person to learn to speak and sing properly again after having surgery.
In summary, if you do not smoke, you may develop vocal nodes anyway. But if you smoke, you are much more likely to encounter this serious problem.
Some people can smoke without visibly damaging or changing their voice. On the other hand, there are professional singers who intentionally cultivated the husky, raspy sound that is the result of smoking for years.
Tobacco is highly addictive and its effects on the sound of the voice will be unpredictable for someone starting to smoke. If you discover that smoking is changing the sound of your singing voice, and you do not like how the sound of your voice is changing, it may be difficult to overcome the addiction and stop smoking.