That's easy to answer: speed and printout size. For example the entire documentation
for dvips (49 pages) takes under 40 seconds to print on my A5000, the printout size
is under 1MB and yes that's at 600 dpi. Who needs PostScript?
Usually drivers like this have the disadvantage that they don't support
platform-dependent stuff such as diagrams. But I added support for that as well so now
you get the best of both worlds. The only disadvantage is you'll have to use it from the
command line.