If you can think of other uses of ChatGPT in regards to writing let me know, but every use I think of falls into one of those.
Ethan Mollick describes using AI to overcome writers block in https://oneusefulthing.substack.com/p/how-to-use-ai-to-unstick-yourself
I guess you might class this as a form of Research Assistant? Either way, Mollick writes useful articles for anyone interested in AI for writers.