Here is a video from NVIDIA explaining one aspect of graphics settings. In short, due to the limitations of presenting images that are broken down into pixels, lines at an angle cannot be represented as true 'straight' lines. If you look very closely, diagonals are actually pixels forming a 'staircase' pattern. For those of you who ever played around with Microsoft Paint or Photoshop, you should know what I'm talking about.
Anti-Aliasing and MFAA
@DanteL I'm sure you're still aware of how enthusiasts love their numbers and specs and new shiny things. It definitely remains a criteria for all those computer performance purists out there. Personally, graphic fidelity isn't a huge deal for me, but I sure love the maths behind all of it. SCIENCE!