The MBTI is mostly useless, because it's a binary schema. Knowing whether someone is slightly more or slightly less introverted than average has extremely limit

The MBTI is mostly useless, because it's a binary schema. Knowing whether someone is slightly more or slightly less introverted than average has extremely limited utility; knowing that someone is exceptionally introverted or exceptionally extroverted is often highly useful. Isabel Myers explicitly argued that the direction of preference is more significant than the degree of preference, which runs entirely counter to the basic principles of modern psychology. Whatever merits MBTI may or may not have, one thing is abundantly clear - we have far better personality metrics available.