To have a single self-contained computer with enough resolution to work with 2, 3 or 4 windows comfortably (in a keyboard-driven way like SizeUp.app, of course)

To have a single self-contained computer with enough resolution to work with 2, 3 or 4 windows comfortably (in a keyboard-driven way like SizeUp.app, of course). Remember the 15 is actually 15.4", so it's less than a 2" difference.