To
re-cap on lateral stability, assume the right wing drops with a swept wing
aircraft. Well if you picture the relative airflow approaching the low wing
(right wing) in the sideslip to the right, the CL increases and the Aspect
ratio increases on the low right wing, because with a swept wing the low wing
effectively becomes a straight wing, and the high wing becomes more swept. That
means a big increase in lift on the low wing so it rolls the wings level, to
the left.
Now if you apply that to directional stability, picture a cross wind from the
right. That is same as the scenario above but the aircraft does not know it is
a cross wind, so it will do exactly the same, it will roll the aircraft to the
left. That again is lateral stability.
But if you increase lift, you increase drag, so directionally the nose will
want to yaw into the airflow as there is more drag on the right wing.
This is a very small factor compared to the directional stability provided by
the vertical fin but it does contribute to it. So it is positive.