This info really struck a cord in me because I always use triple dots, double dash or parenthesis in place of the em dash. I guess I need to slowly change that, at least in formal writing if I ever have to.
This is a tip from Daily Writing Tips.
Em dashes are the width of (you guessed it) a capital M. Most often, they’re used in pairs to emphasize an element or elements within a sentence:
Cruciferous vegetables—broccoli, cabbage, and cauliflower, for instance—are said to lower the risk of cancer.
Em dashes can also show an abrupt change in thought:
I thought I had time—more than enough time—to catch the train.
Or they can show interrupted dialogue:
“I told you I can’t—”
“You mean you won’t, not can’t,” she said.