Just this morning I listened to a radio interview with pianist Igor Levit. It was excruciating. He had to think for seconds before every third word in a sentence, creating awkward pauses, and when he had finally finished an answer, he had only transmitted trivial content. I am sure that if they had sent him the questions a few days earlier, he could have prepared much more interesting and eloquent answers. I felt very bad for him, because I recognized myself. If you ask me a question I haven't thought of, I
usually have an answer ready immediately. The problem is that I either don't like the answer, or don't know if the answer is correct, and I would like to have time to refine it, think about it, check it.
Major problems then arise if I have already started to answer the question to avoid an awkward pause, and realize several words in I don't like the answer. Finding a way out of the words you have started then feels like texting while driving along the road with 100 km/h.
I have been in several interview situations in my life (including two on national radio), and the ones that went well were usually the ones where I either knew the questions beforehand, or in which I was asked questions I had already thought of and memorized an interesting answer.