It makes things crisp enough that those higher resolutions are practical. Sure, you can turn your font size down low with a low res screen, but you rapidly get

It makes things crisp enough that those higher resolutions are practical. Sure, you can turn your font size down low with a low res screen, but you rapidly get to a point where the characters are harder to distinguish. Not so with the retina screens. Really you just have to see the difference. It's striking.