I'm a luddite when it comes to generative AI models but to me it seems like the primary use case for training OpenAI on Reddit posts would be if you wanted to be able to create a more realistic genAI bot to post on Reddit for some reason.

Surely if you are making a genAI bot for medical/legal applications the likelihood of hallucinations/misinformation is way higher if Reddit posts are included than if it were solely trained on official medical/legal documents