Either the above link or XXX-Main Chassis Tuning guide are good references for those who wanna learn tuning.
Sosidge has it right, but let me try to further clarify Roll Center:
The lower you have it, i.e. the higher you raise your inner camber links or raise your pivot blocks; the more chassis roll you'll have. This situation is better for low-grip situations, like unprepped asphalt.
The higher you have it, i.e, the lower you put the inner camber link position, or the closer you put your pivot blocks to the chassis,; the less chassis roll you'll have. This situation is better for high-grip situations, like carpet.
Manipulating only the roll center won't make your car dialed. You also have to consider shock angle, camber, tire grip, arm sweep, caster, and a host of other variables too long to list. Just remember to start with the box setup, and make each change, one at a time.