I think its good to pull down dragons if you dont already have that shout is it?
This is how I used it, and it was for the first time. What was funny is I managed to kill the dragon before the shout ran out, so it continued to strike my companion even after the fight was won. He kept warning:
"What are you doing?"
"I'm warning you!"
"This is the last time I'm telling you!"
"Arggh!"
And that was the end of poor Marcurio.