its not meant to kill its what you do to the poor fools while they are incapacitated that is the real damage
Exactly, Fus Ro Dah has saved me during many a boss fight when I send the baddie clattering against the back wall of a dungeon. In fact, some battles I've been in were probably completely un-winnable for me, save that one shout.
At the very least, it can get a very tough opponent of your back and let you catch a breather for a sec. Plus, watching all the other stuff in the room scatter about is always fun. Hahah, love Unrelenting Force so much.