Robert is referring to the ignition advance resistor that is discussed to death in the Performance Paddock.
The long and short of it is; there is a resistor ty wrapped to the a/c line near the master cylinder. When you remove it, you add 6 degrees ignition advance. On Euro cars there is a rotary switch that allows adjustment for varying octanes. On the US cars, this resistor retards the maximum ignition advance for emmissions reasons.
There is no real downside to removing it because these engines have a knock sensor that prevents preignition problems.