The value that the graphical pieces provide is that they are interactive. The graphical pieces build up to the one where you control both parameters simultaneo

The value that the graphical pieces provide is that they are interactive. The graphical pieces build up to the one where you control both parameters simultaneously, and see how you can halve the throughput of the system by seemingly innocuous changes. The whole point is that the cause of the slowdowns is not obvious because the effect of the changes is non-linear. Sure, you can take the author's word for it - but with the neat simulation, you don't have to. You can see the model in front of your eyes.