Very broadly, in the "has the concussion caused permanent damage?" or "is your child suffering from debilitating lead poisoning?" sense. It's good for diagnosing disability. But the joke of it is that high IQs (and we're talking legitimately high, not I-took-some-bullshit-test-online high) don't correlate with specific academic or economic or social aptitudes.

Langan's high IQ had not led to greater success in life – Langan has no degree, having twice dropped out of college. The book compared him with J. Robert Oppenheimer and focused on the influence of their respective environments on success.

Langan has spent many years working on his idea that he calls the "cognitive-theoretic model of the universe" which proposes that reality is a self-simulation. He self-published a book about it in 2002. In interviews and self-published writings, he has expressed beliefs in a variety of fringe proposals and conspiracy theories, including arguing in favor of eugenics to prevent "genomic degradation", opposition to interracial relationships, and support for the 9/11 truth movement. His political opinions have gained him a following among the alt-right.

Turns out the natural ability to quickly identify the correct subsequent pattern in a series of patterns only gets you so far.