You do it in medium to strong wind conditions, if you have rudders that are tending to have a spin out. Rudders are twisted in the water, if they are not made from Carbon. The drag and the spape of the standard rudders and the black EPO rudders also cause cavitation.
All this is reduced, if you lift one rudder in more wind.
In light wind conditions, it does not help at all.
Also invite to our seminar, see www.hobiefleet32.org
We will address all these things there.

Fritz