[ghusto]

Emdash separates, hyphen concatonates, endash is the one that seems superfluous.

Emdash is actually what people mean a lot of the time when they use parenthesis.

[johnea]

If it's supposed to separate, then it should be surrounded with spaces...

[ghusto]

Either is acceptable: https://www.merriam-webster.com/grammar/em-dash-en-dash-how-...

Also, a comma is a pause — and what a wonderful thing — whilst an emdash is a tangent.