As a result, a hallmark of GPT-generated text is its (over)using of the em dash--I have stopped using it for this reason an just use two hyphens now instead.
Em dashes allow me to get multiple ideas into a sentence with comparatve ease and have it still make sense. Otherwise I'd have to add additional sentences to a paragraph which itself has issues. With a longer paragraph one has to worry about its readability and comprehensibility, and that means having to restructure it—remove redundancies, etc.—and that takes time.
Good writers can think ahead and do all that restructuring in their heads. When writing about an idea, concept or logical unit thereof they'll write out short, coherent and readable text all in one go, and it will make sense. I only wish I could do that.
As I see it, em dashes are more a crux for bad writers like me (they allow our text to be at least comprehensible).