Mast is strongest in fore-aft plane and the loads on the mast are highest in the sideways plane. So more rotation will bring the strong plane of the mast more in line with the plane of highest loads. Pretty the forces on the upwind leg are the highest and here the sideways forces are 3 to 4 times as large as the fore-aft forces.

In reply to mast rotation. In big winds the way the stays are attached to the mast also help rotate it. This means that the amount needed to properly rotate the mast can be pretty small. In light winds you need the mainsheet to keep the mast properly rotated but here the mast loads are way lower. So in general the load from the boom (with an adjustable mainsheet angle as you have) can be considered pretty small. Unless you trim the mainsheet angled way back adn have the rotation limiter take up alot of load.

Wouter