It goes still farther. Gilt has a postscript library. This library defines all kind of useful functions. Mathematical functions, Complex numbers, useful shapes. They are all there with a perfect quality.
Gilt is exact.
This should be clear by now. If you want a box to be 10 mm wide, write 10 mm and you get it. Write Red setrgbcolor and you get a red. No hidden traps. No more moving parts of pictures around to get them centered.