In many kinds of writing, perhaps most, communicating your state of mind to the reader is a primary goal. Even a smart LLM fundamentally degrades this, because to whatever degree that it has a mind it isn't shaped like yours or mine. I've had a number of experiences this year where I get to the end of a grammatical, well-structured technical document, only to find that it was completely useless because it recited a bunch of facts and analyses but failed to convey what the author was thinking as they wrote it.

(Of course, that may well be exactly what you're looking for if you're writing an audit report or something.)