Originally Posted by
furballi
One leg is usually stronger than the other. Rotating the saddle optimizes the sweet spots at the rear of the saddle and reduces the chance of one thigh rubbing against the front/mid-section of the saddle.
Only problem is that rotating saddle, say, to the right would theoretically decrease rubbing against mid-portion of the skirt but increase rubbing from the front-nose part. With plastic saddles I always kept them dead straight with no asymmetry problem. Used to do bike messengering on cheapo stock/discount bin sport-touring type saddles with little problem.