They are often used to convey urgency: “Help! I’ve fallen and I can’t get up!”
Or command: “Stop the train! Or I will shoot you dead!”
Or astonishment: “Wow! Did you see that flying thing?”
Or shouting: “Come down! The roof is collapsing!”
Or telling the reader that something is funny: “I was smoking a joint and the cop walked right by me!”
So what to make of writers who employ multiple exclamation marks (EMs) as in: “Come down!!! The roof is collapsing!!!”
Does the use of three EMs mean the peril is three times bigger? The urgency three times greater? No, but it does mean the writer is trying to indicate that the danger is very, very great and the collapse is imminent. It also means that this writer is going to be taken as an amateur by people in the book industry who recognize that the use of multiple EMs is a sign of a writer using a crutch with a point on the end.
Use your words, guys: “Come down! The roof is collapsing!” The implosion happened so quickly that it was over with a loud boom before the words were out of Sean’s mouth. Debris rained and a huge cloud of dust obscured the people standing on the roof – or would have if they had still been there.
Even single EMs should be used sparingly. In non-fiction, they should not be used at all. In a novel, they should be confined to dialogue and to first person narration. And they should never, ever be used to indicate humor because that is tantamount to holding up a laugh card while you snicker at your own joke.