[Hoasi]

You have to understand how something works to be able to depict it properly in an illustration. Understanding is the key to explain anything to other people. An illustrated cross section can teach the complexity of natural or engineered objects in a way that photography just can't.

[thaumasiotes]

The opposite is true; understanding how something works usually interferes with your ability to draw it accurately. People want to draw the truth they know rather than the image they see.

And contrast idiot savants who are able to draw images perfectly, while no one believes they need to understand how whatever they're drawing works.

[Hoasi]

That started as a good counterpoint. But you need to understand how something works to be able to draw a cross-section from scratch. It represents a truth that is not otherwise visible. Even to draw a basic diagram, you must understand what is at stake. What an idiot savant draws or paints, no matter how realistic, is a very different job.