Just because you didn't use it doesn't mean that other's didn't. I personally used it a lot in Halo Anniversary. The instant switch is an amazing way to show you the technical leaps that have been made over the past 10 years. I loved walking around the maps, and switching back and forth to make comparisons to what 343 had done with the game. You wouldn't get the same effect if you have to quit out, change a setting in the menu, and then load back in. It makes the whole process not worth it.

Could you seriously even tell the difference if there was only a small change in the resolution? It seems dumb to remove a feature as amazing as the graphics switching in order to get a tiny bit more resolution out of the image.