Eliciting and concept checking

Eliciting and concept checking form an important part of teacher talk, at least according to some. But what are they? Are they really necessary? How do you do them well? Why bother? What's the point the point of asking redundant questions that you already know the answers to, like this one? Would anyone ever do that? Well, teachers do, and students don't seem to mind, and there is a possibility that we sound like pompous idiots. But possibly not. So, let's waffle about these questions about questions to find the answers that might be the answers to all answers.