When people come to hear you speak, they expect two things: to hear your presentation and to raise questions about it. They may wish to know more about the subject, or they may want to contest some points. It's true that when you permit questions, you risk losing control to the audience, because for that moment the questioner is in the driver's seat. But remember that as the speaker you are automatically in a position of authority and you have the advantage. If you handle the questions—and the questioners—well, you extend the power of your speech and leave your audience not only informed but also impressed.
Your objective is to retain as much control for yourself as possible. You can say, "I will take any reasonable question on the information I'm sharing with you." Later on, if you get a difficult question, you can humorously add, "I said any reasonable question," and move on. The main drawbacks of the question period are your risk of being exposed to questions for which you are not prepared and the danger that questions may come from unfriendly, or even hostile, members of the audience. But you can virtually eliminate these risks through careful preparation.