I think I've seen a thread about it here, did they give any helpful advice about CFS?
Personally I've found it very helpful. I use it for a myriad of ME/CFS related things.
If there's a new research paper, sometimes I don't have the cognitive ability to read through it and I'll have GPT4 read it and give me a summary of relevant aspects. Then I can ask it questions about what I don't understand.
I'll often ask about specific supplements, pathways, and so forth.
Always good to keep in mind that it's not infallible, it'll make mistakes, etc. But it's great for asking questions about stuff you don't understand, etc. I keep forgetting stuff, so I have to ask it about microglial activation or endoplasmic reticulum stress or whatever.
I think people don't realize how good it is at explaining things, distilling stuff, etc. It's a terrible search engine (not what it's for), but a great teacher.