Square setup, assuming it's achieved via larger fronts, will increase your front grip to dial out some understeer. It would also allow you to rotate your tires (I recommend only front to back, not side to side).
Staggered looks cooler to some people and is part of the built-in understeer that BMW puts into its cars, which they do because they want to minimize incidents of people who don't know how to drive buying their cars, turning DSC off despite not being able to drive, and then going careening backwards off the road and giving BMW a reputation for building death traps.
Seriously though, while dialing out understeer sounds cool and everyone loves more grip, understeer is built in because it's an effective early warning system that you're exceeding the grip limits of the car and possibly just plain driving poorly, and losing grip via understeer is far easier and more intuitive to recover from than oversteer -- so be honest with yourself as to how good a driver you are before you start down that path. For example, have you attended several track events?