Well em-dashes can be used in place of other punctuation that is typically used to denote parenthetical information — such as commas and parentheses — but it also has other uses. Similar to a semicolon it can also be used when changing the idea of a sentence — it's versatile and often an overlooked and underutilized piece of punctuation. Additionally, when you have multiple parenthenthical levels, such as this which is commonly placed within commas — or parentheses — which can be overused, it allows you to segment different layers of parenthetical information.