I can't allow LLMs write my messages in any language I'm fluent in. They just don't sound like me at all. It would feel dirty and dishonest to send that slop out.
They can be good at grammar checks, but even then I wouldn't fix quite everything, it's better to let some of my natural flaws go through.
My wife translated some text she had written in her own language to my native language, as she didn't feel she could do it. I found grammar errors, surprising ones. I found places where pronouns were used so far into the sentence that a reader would be lost finding what that pronoun actually referred to. And more. In the end I rewrote the LLM-generated text myself, many pages of it.