"Only good reason I can think of is where multiple shots are required to weaken / overcome some kind of hardened defense."

If there's a simple window, you can kill everyone along the wall by a simple application of a high-precision-timed grenade. "Explode 50 cm behind the window" is simple to achieve these days: http://en.wikipedia.org/wiki/XM25_CDTE , http://www.youtube.com/watch?v=Fgh4uy5A-lI