The question "why is this useful?" is akin to "why do we like a thing?" and liking a thing is an opinion, and the reason for liking something carries a motivation, which differs from simply knowing what a thing is.

Why is it objectively useful? Well, it's not. Idempotency is neutral. It can be as useless as it is useful. Knowing what it is matters more than a cargo cult desire to find utility in a vocabulary quiz.

Should a test verify that an individual's opinion aligns with a trend expressing a point of view, or should it verify awareness of concepts?