Because the dash marks a strong break, it alerts the reader to the importance of the material that follows it.
Use a dash or a pair of dashes to emphasize a definition, a dramatic statement, a personal comment, or an explanation.
Consider inserting a dash or a pair of dashes to emphasize a list.
If the list appears in the middle of the sentence, use one dash at the beginning and another at the end to signal exactly where the list begins and ends.