It's a two-way street. When someone tells you "don't do that", they usually mean they don't want to be on the receiving end of what often amounts to LLM-powered literary diarrhea.

Yes, in theory, the quality can be the same or better than human output. In practice, the tool creates two problems: it's too easy to produce walls of text for no compelling reason, placing asymmetric burden on the recipients; and it's too tempting to click "send" without reading because you're "90% sure" the email / doc is correct, wasting everyone's time multiple times every week when it isn't.