It's such an annoying thing. I never used them in English, but in English they are mostly intonational. In Russian em-dashes are grammatical, you have to use them, in most cases ommiting them is a mistake, in some cases it changes the meaning of the sentence.

People were already telling me that using proper grammar is weird long before slop machines came to be. Now they have an actual reason to be suspicious, I, myself, wouldn't want to speak with someone who uses LLMs when casually exchanging messages.

Never would I ever think that investing time into learning how to write properly would backfire like this.