If you have a follower, make them "wait there" with your char. Then go ahead and cast or shoot. I used the Stormcall when going after Alduin to knock off the Draugr guard's. The Sunhallowed Arrow's I used when attempting to reduce the amount of opponent's such as the Forsworn, or banidt's who hide in broken down castle's or fortresses. Those work well knocking off any archer's on the wall's.