Camber isn't just there to keep the wheel upright as the car rolls. Even with no body roll, more camber gives more cornering grip due to camber thrust (up to a point - every tyre will have a peak camber at which it gives maximum grip). Look at the front wheels of an F1 car; they have loads of camber even though there is almost no body roll.
So the ideal setup for maximum cornering force is one with the static camber at the peak for the tyre, and the camber gain set to keep this amount of camber throughout the cornering process. In practice this is never possible as it will be affected by tyre wear, desired roll centres, and keeping the wheel upright for maximum traction under acceleration and braking.
So like all setup parameters, it's a comprimise.
RC-Timing Software - http://www.rc-timing.com
Mercedes AMG F1 - http://www.mercedes-amg-f1.com/