Well, that's the thing about the em-dash - it has always been usable as a "swiss army knife" punctuation mark.
Strictly speaking, an em-dash is never needed; it could always be a comma or semicolon or parentheses instead. Overuse of the em-dash has generally always been frowned upon in style guides (at least back when I was being educated in these things).
Strictly speaking — an em-dash is never needed; it could always be a comma — or semicolon — or parentheses — instead. Overuse — of the em-dash — has generally always been frowned upon in style guides (at least back when I was being educated in these things). ——
Strictly speaking, an em-dash is never needed; it could always be a comma or semicolon or parentheses instead. Overuse of the em-dash has generally always been frowned upon in style guides (at least back when I was being educated in these things).