As you change the load on your rudders, you also change, ever so slightly, the angle of attack of the daggerboards and hulls through the water. The proper angle of attack of the daggerboards will help generate proper lift to windward with minimal drag. With the proper amount of pressure applied to the underwater foils, leeway will be virtually eliminated allowing the hulls to track straight, and more efficiently, through the water.

In addition, a swept back wing profile is more efficient through the wind providing less forward drag...hence raking the mast back works a little better for speed but at the expense of a little power. A straighter wing profile will provide better lift (more power) so less rake is better for lighter airs.