I would also add that it is useful because most people do not speak with textbook perfect grammar. I recall a team leader telling an interpreter to "tell that a-hole to get the f out of my face and start singing. We know this s*** is here. He can show us or we can turn the f-ing s-hole upside-down."
If English is not your first language, then you might have difficulty understanding what that means, especially if it is a tense situation and you're a little flustered.
Bookmarks