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.
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.