Em-dashes are only incidentally related to contrasting statements like that, too. My main use of them is quasi-parenthetical interpolation. It can be nice when you want more emphasis on the aside, or just to avoid using parens or commas if you started writing something that already uses them.

My usage is not just parentheticals—when they're used like this—it's ironically continuations — a turn the sentence takes but not really standalone.

And the continuations… Honestly? They'll never <|im_end|>.

// • Chronic option-dash and option-shift-dash user, option-[ or option-shift-[ as well as option-] and option-shift-] — not to mention option-8 and option-; …