One that jumps immediately to mind is IQ testing used for epidemiology, such as exposure to toxins and the effects on children. IQ tests were used in the original study (Phillip Landrigan) used to show how leaded gasoline causes cognitive imparement in children. For things that cause sub-clinical imparement, you need a way to test for lowered intelligence, that doesn't rise to disability level.

That's a few million, if not billion people who's lives have been improved by having IQ tests that were used to force environmental regulation worldwide.

The trends of removing lead from gasoline and such were already happening prior to IQ being used as evidence. In fact, the only way IQ could be used as evidence would be for the lead to already have started to be removed. So, using IQ for such was a data point, but it was not the cause of the movement.