The point, I believe, is that sometimes generating bullshit requires some understanding, so it is a worthwhile exercise. Just like running: you end up where you started, so it may seem that you did nothing. But obviously you exercised.

Asking a student to write an essay is similar: it is an exercise. Of course that essay won't be published or read by anyone else, but that was not the point. Just like you were not running somewhere, you were just running for running.