Key adjust for separate translate X and Y keys had a bug, so revaluing is unlikely to make sense. We've fixed it in 4.3.20-beta, which will be available today.
Revaluing is most useful when moving a single key up/down. When moving multiple adjacent keys it can't do as much, because handles between the moving keys are preserved.
Key adjust is useful for editing multiple keys by manipulating bones in the viewport. It used to be the only way to edit multiple keys at once, but now that we have the graph you can simply select multiple keys and move them all up/down. Still, sometimes key adjust is more convenient.
