The answer to that question is in the final clause, which is “unless with the permission of the member who has the floor”. If you ask a short question and the witness says, “Look, I'd love to give you more information; I just don't have enough time,” then you could say, “Sure, please help yourself. Take your time.”
It does create an equality of time, so that the witness and the questioner get the same amount of time in each block and we don't have a 15-second question followed by a three-minute, unrelated answer.