In a perfect world, we would be able to have a ceiling fan in every room of our house, so we could be cool no matter where we go. Since that would get too expensive and would look excessive, we have to decide where we want our ceiling fans to go.
The best bet is to put one to three throughout your house in the rooms you frequent most, or a room that desperately needs it. A room that is naturally cool would not necessarily need a fan, but one that is unusually hot would suit a ceiling fan perfectly. You do not want to overdo it, but you want to have an excellent level of comfort as well.