I mean, if you're a self-hosted enthusiast, I don't think that project is what you are looking for, it's just the UI that is self-hosted, the meat of the project is still hosted at OpenAI so not that useful for self-hosted enthusiasts.
Sometimes the ChatGPT UI has gone down while the API has been unaffected (like yesterday). Also GPT-4 via the API is much faster. That's the point of using an alternative UI. As for self-hosting it, that's just to ensure it doesn't go away I suppose.