I realize that it will have more or less dramatic effects depending on the site, but in the two examples that Adam Schwartz chose to best demonstrate the effect, it seems to be just "remove shading and gradients." Why? Is someone out there offended by gradients? Why would you care?

Edit: Or is that the point, that it's meant to be a commentary on a design aesthetic? afschwartz's own cryptic response in this comment page suggests that it might be.

If so, the commentary seems to have escaped some commentators--one comment on the original says "Github looks much nicer with it enabled." Huh? I had to look at the side-by-side GitHub comparison for several seconds before I even saw the difference.