This is exactly how I use them too! What I usually do is give the LLM bullet points or an outline of what I want to say, let it generate a first attempt at it, and then reshape and rewrite what I don’t like (which is often most of it). I think, more than anything, it just helps me to quickly get past that “staring at a blank page” stage.
I do something similar: give it a bunch of ideas I have or a general point form structure, have it help me simplify and organize those notes into something more structured, then I write it out myself.