With the introduction of the Fifth Generation Mustang in 2005, the time tested 8.8" Ford Differential received renewed interest in it's performance capabilities.  One of the hottest new performance modifications in the last few years is lighting driveline components to improve performance.  Similar to the practice of lighting flywheels in the Sport Compact Market, lighting the Ring & Pinion is done to deliver as much horsepower to the wheels as possible.
The horsepower delivered by your engine is set.  Installing a lightened gear set will not increase horsepower, what it does is reduce the energy needed to get things going. referred to as the "Moment of Inertia", the MOI of an object in determined by its mass and diameter, more power is needed to begin and maintain motion in relation to how larger and heaver the object is.  Installing a lightened Ring & Pinion of the same ratio will take less energy to begin and maintain movement.  This allows horsepower to be used more efficiently.  One of the greatest advantages of affecting a change to your vehicles MOI is that it improves performance throughout the entire "power curve".  Combining performance upgrades like a lightweight Driveshaft, Ring & Pinion and other components will help deliver the power at all speeds. 
New engineering processes have allowed ring and pinions to be "designed light" prior to heat-treating.  This provides performance, easy set-up and quiet operation.  National Drivetrain offers many lightened ratios for all 8.8" & 9" Ford applications