When a speaker uses a lot of rhetorical questions, it amounts to an admission: “Since I am not letting you ask any questions, let me give you a few that you can pretend you asked.” And: “You are probably bored, so let me try to pique your curiousity.”

Once in a great while a rhetorical question can just be good rhetoric. Usually, the best rhetoric prompts the question in the listener’s mind without stating it baldly, and answers the question without disrupting the flow of thought.