Here's a little discussed topic of interest. Men just love to write with lots and lots of dashes—. Women avoid using, or even reading, dashes if they can, as if to say, "Hark! what manner of hellish fiend poketh forth at me?"
Why do men use dashes so much? Probably because a dash implies a forcefulness that other punctuation types—except for the exclamation point—do not! And you know us men; we're all about domineering!
We mostly use em dashes in the USA. Style manuals (the evil beasts!) do generally have specific rules when using en – verses em — dashes, but I find more often than not that most people dispose of those nasty rules and simply use em dashes and hyphens for everything, the main reason being that the en dash is not much longer than a hyphen - and people often confuse the two while reading. The main use of the en dash was always to indicate a range between two things such as months or years. Thus April–June means from April to (or through) June. However, many people do indeed use a hyphen for this: April - June. They generally will place spaces around the hyphen when doing so, but some people don't bother: April-June, and we all know what they mean just the same. Most word processors don't have a keyboard character for either the en or em dash, and this is probably the reason why people have largely dropped the en dash in favor of the hyphen nowadays. Word processors do, however, generally have an insert function for dashes, meaning that you can choose a dash from some kind of "insert" drop down menu where you can choose to insert a "special character" such as a dash. MS-Word has a great feature for inserting em dashes automatically, although you may have to turn it on in "options". If this is turned on, then you merely need to type two hyphens in a row --, and they will automatically be turned into a single em dash —. Pretty nifty, eh? Of course my version of Word is fourteen years old, so yours may treat em dashes differently.
Now, what can a dash do? I'm glad you asked, my punctuation starved friend. There are many things it can do, but the greatest among these is that it can replace many other kinds of punctuation, thereby making the chore of writing less of a chore. And what man isn't in favor of less chores? I can nearly always tell a man's writing from a woman's because women will inevitably look for the hardest way to say something, both stylistically and grammatically, that they can. Thus their papers are full of commas, colons, ellipses, and parentheses when a simple em dash could often be used in their stead. Now any fool knows that you need to use some variety when writing, so I'm obviously not saying that you should always use a dash in place of these other punctuation marks. But men do tend to use dashes quite a bit while women ignore everything about them.
The thing that need be remembered about the mighty dash is that it is indeed mighty! It's often used to set off a thought in the middle of a sentence just as a parenthesis would, but when a dash is used, it generally has a forcefulness about. It almost causes you to see exclamation marks even when they aren't present. For example:
Ron Paul is running for president yet again—the whacko—much to the chagrin of sane republicans.
See what I mean? Women tend to tip-toe around controversy though and would rather whisper their snide remarks:
Ron Paul is running for president yet again (the whacko) much to the chagrin of sane republicans.
It's almost as if the clause inside the parenthesis is the writer whispering in your ear.
It's the same when using a dash in place of a colon. A colon is the sissy version of a dash. It's a suggestion. A dash is a command! Let's say we're leaving a note for our son on the fridge:
Bobby, before you leave the house today, you have a few chores: clean your room; mow the lawn; and practice your trumpet lesson.
Bobby, before you leave the house today, you have a few chores—clean your room; mow the lawn; and practice your trumpet lesson.
In this case it's kind of subtle, but I think you can still see where the dash makes the list of chores more forceful.
Where the forcefulness of the dash really shines though is near the end of a sentence when setting off a phrase:
He was a great American—in his own mind.
Or:
She thought she could resist my good looks and charm—foolish girl.
And lastly, though many people frown on it, a dash can be used to show a thought trailing off at the end of a sentence:
I was left for dead, and nearly did give up on living, until I thought of him living it up on my dime, so—.
This last example is one in which I have never once come upon a piece of writing by a woman where she used a dash. (The lesser sex will use an ellipsis every time—shhh.)
