What would you replace it with? While it's not a good metric for individuals, in group studies, it's a useful proxy for information processing intelligence.

My understanding is it was originally made for figuring out what grade a child belonged in. Like if a kid came to a school, what grade do you put them in? Give the IQ (intelligence quotient) test to determine what grade they go in. Take what they know (score on top) divided by what you expect them to know at that age (score on bottom) gives you a quotient for choosing what grade to place them in. Highly educated? Higher grade. Lower education? Lower grade. Fast learner? Jump a grade. Slower learner? Redo a grade.

Seems like it used to be a useful tool. I don't think that's how society uses it anymore, but from the start, I bet it probably worked ok.

Why? Just on principle?