The only thing I've noticed is that the dry flies don't stay dry as long! Most of the time the fish are not even aware that it's raining since 95% of their feeding is subsurface anyway. It may allow fish in lakes to feel less threatened from birds when it rains hard, like when the wind makes waves so the birds can't see them as well. This will sometimes bring them closer to the surface.
My preferred technique is to fish from my recliner on WFN!
GD