It would ideally be descriptive vs. prescriptive, so you could uncover things like "we get mainly recent-college-grads applying, but our strongest employees are those who joined mid-career", or "we have very few minorities who apply, but those who apply and are offered positions tend to be strong and stay with the company a long time".
Pretty meaningless unless you are hiring at Google scale, though.
Many big corporates have psychometricians on staff. At least one even has a department dedicated to psychometric testing.
There's plenty of demand for skilled developers so I don't understand why people put themselves through the humiliation. I expect that a lot of skilled people self-select out of these sorts of psychometric processes if they can, to the detriment of potential employers.
I also wouldn't be surprised if many of the tests contain an element of uncorrected racial/cultural bias, and the psychometric industry has been exploiting the inability of the government to enforce the law (Employment Equity Act), which makes discriminatory testing illegal.
