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 a

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). ——