The real world is not flat. So why should the world of Minecraft be? But obviously, there are no curves in Minecraft, so that is a little bit unrealistic. So some guy decided to fix that and make the world of Minecraft a little bit more realistic, or maybe too realistic. The Parabolic Shaders, like in its name, makes your Minecraft world a little bit curvy. Though it does not make your world a sphere like it should be, but rather a parabolic. Your moving mechanism would still remain the same, though. Just expect a little dizziness while walking.
All credit goes to stduhpf