Use an em dash to show a strong break in thought
Use an em dash to add emphasis
Use an em dash to set off parenthetical information
Use an em dash to indicate an abrupt interruption
Use an em dash to replace commas, parentheses, or colons when stronger separation is needed
Use an em dash to introduce a summary or explanation
Use an em dash to signal an unfinished thought
Use an em dash with no spaces in some style guides
Use an em dash with spaces in some style guides
Use an em dash consistently according to the style you follow