Originally Posted by TDP

This subject gets over-analyzed way too often & blown out of proportion. It's really a minimal difference. Most aftermarket clutches have a pressure plate that is much heavier than stock, so a light flywheel will more than make up for it. For example, my Diamond Clutch kits all weigh right around 43lbs. This is the total weight of the disc, pressure plate, and flywheel. Keep in mind that I use the 15lb lightweight chromoly flywheel with all my kits. Then I weighed a stock clutch kit and it came out to 49lbs. That is only a 12% difference in overall weight. Its just enough to feel a noticable difference. With the rotating mass being 12% lighter, the engine effeciency is increased. The advantages that you will see include; better power transfer thru the drivetrain equating to a slight gain in RWHP, RPMs climb faster, RPMs drop faster.
Disadvantages are; Less weight will give you less momentum when racing. So it will be a little more tough to get a good launch.
However, the advantage of having better engine effiency by far outweighs this disadvantage.
Considering the few trade-offs when using a lightweight flywheel, it is worth it, hands down.