While many smokers are considerate about their usage, there are unfortunately some that do not understand why others want nothing to do with it. While I won't go into some of the frankly horrible interactions I have had with these types of smokers, I will say that when it comes to having them in a rental property or apartment building it really can be a messy situation.
At the root of the situation, the decision is yours. It is your property and if you state that you do not want your resident smoking in it, then that's that. However, sometimes people will smoke anyway. What do you do in this situation? Well, one thing that we always suggest is to have a clause in the lease similar to a hotel room that is non-smoking. State that if someone is found smoking or there is probable cause to believe that smoking has gone on in the apartment, a fine will be charged to the resident(s). This is something that will hopefully discourage anyone from going behind your back and filling the area with smoke.
While allowing smoking in your building may allow a wider range of people to rent from you, you will need to think long term. Smoke can seep into wood and walls and can cause a smell to reappear years down the line, especially when the temperature warms up quickly. I periodically have to open all of my cabinets and air them out because the last resident in my apartment smoked heavily and the smell was trapped. There is more to allowing smoking than just what is happening in the moment. While it is your choice, make sure that you have thought of the outcome of each decision before settling on whether you allow smoking or not.