There is a direct correlation between suspension travel and camber.

Your suspension doesn't move perfectly vertical it "cambers" (travels in an arc) in and out while moving up and down.

When you lower your car you force a stationary portion of travel upon the control arms they compensate by camber to make up for the height.

Depending on how much you want to lower your car (2-3" you said) and the design of the vehicle will dictate how much camber adjustment you will need.

You will probably need at least 1.5* of adjustment for 2 inches lower in the front and 1* for the rear. For 3" lower try 2* of adjustment in the front and 1.5* in the rear. Those should be the right amount for this application.