Under performance there is an option to enable OpenGL, what does this option do?
OpenGL (Open Graphics Library) is a software library that utilizes graphic card hardware to draw computer graphics. If you have OpenGL compatible graphics card in your PC, you will get a visible performance boost when you activate OpenGL in Photoshop. All kind of screen updates (zooming, panning, rotating, rendering the effects) appear sooner and smoother.
ADDENDUM: See, what it's dialog promises
Practically, not much. I think it has smooth zooming, as opposed to stepwise, of the image and probably a couple other enhancements. You also need it for 3D and some non-default filters like normal mapping.
For day to day image manipulation use it doesn't change much, though it can speed up a few view options depending on your gpu. I'd leave it checked unless you have problems.