Today in the New York Times' Opinionator blog there's a love letter of sorts from Ben Yagoda, author and professor of English at the University of Delaware, to the dash. Not the em-dash, in particular—we love you, sugar!—at least not at first, but an homage more generally to the plain old generic slice of punctuation that is oft combined barbarically as two to create a poor man's em-dash. Later in the piece, he acknowledges the superior form, but we'll get to that in a moment. He calls the dash—"the horizontal line formed by typing two hyphens in a row"—the most versatile piece of punctuation of all, unbound by the grammar rules that constrain the others. The em-dash is a special little thing of typographical beauty. It is a thing you will want to incorporate into your writing life. This marks a change of heart for the paper, or at least a diverging opinion from that of New York Times standards editor Philip Corbett, who wrote in 2011 reminding everyone to stop using so many dadgum em-dashes, for the love of God (we paraphrase).
So, how to use it, without seeming a fool? Yagoda advises on the few basic rules of the dash: don't put spaces before or after it (we agree); it's not the same thing as a hyphen (true); the dash can be used for a pause (one per sentence max, he says) or as a parenthetical (two per sentence, he suggests, though that as well as the aforementioned regularity would likely weary a reader, in our opinion). He adds that a dash might function in dialogue to indicate that a conversation drops off or perhaps is interrupted, but to indicate a change in any case. From the Elements of Style, "Use a dash only when a more common mark of punctuation seems inadequate."