Earlier quoted context omitted.
"Write an email that says I did X and they should do Y, but if Z then W, and we should schedule a meeting with P and Q." I feel like for most emails I write, information density is close to a maximum. This means there's no actual gain to be had from a language model. The email I would write myself is going to be about the same length as the prompt I'd have to write anyway.
There is a huge gain if English is your second language, and you use ChatGPT to rewrite, or translate. Even if English is your mother tongue, if your written English is crappy or you need to write in a style you are unfamiliar with (e.g. formal), then ChatGPT can help.
I also think writing yourself might be far better practice. This tool can easily become a crutch. This is unlikely to be free anytime soon. In fact it's likely to be quite expensive.