There are questions students have that are worth hearing. It's not very beneficial to grind the lecture to a half every two minutes for one, but that rarely happens. If somebody in the crowd has a question based off of something that was just said, they likely aren't alone and everybody can benefit from an explanation.
I'm currently a college student and I am much more engaged in the class if the professor keeps the class engaged. If the professor is asking the class questions and letting them participate, then generally the students respond well. If there is a chance of the teacher calling on you, I feel like most people want to pay attention and know the right answer.