I attended a lecture, many years ago now, where the lecturer, a colleague of mine, talked for an hour with only one visual aid: the diagram on the left, drawn by hand on a whiteboard.
His lecture was about what we, as designers, were to achieve. The arrow coming into the box denoted what we were given. The box itself denoted what we were to do with the given. And the arrow leaving the box denoted what we were to produce by our efforts.
Of course, the lecturer gave details of the particular artefacts we were to design, adding substance to his presentation, which was animated by his bouncing around in front of the diagram, first pointing here, then pointing there, as he made each particular recommendation. The hour just passed in an instant. He used no notes. He was clearly totally committed. I was enthralled.
But without the visual aid, I doubt it would have worked at all.