The 4 shoes of the werks clutch provide more contact area than a 3 shoe clutch. This will give the clutch better grab. A heavy clutch is one that engages sooner. A light clutch is one that engages later. A lighter clutch will allow the engine to spool up before engaging for a more aggressive launch. The werks clutch is not just light or heavy, it's adjustable for everything in between.
There are three types of shoes, teflon, carbon, and rulon. Teflon is the hardest material and for off roading, is used when the surface is slippery or low traction conditions. It also lasts the longest. Carbon is a good all around shoe, with good wear and grab. Rulon is the softest and has the most grab but tends to wear very quickly. With rulon you also need to adjust the clutch to compensate for heat build up.