Really the best use I’ve personally had with ChatGPT is having it take on the role of DM and 3 other players so I can play Shadowrun and D&D by myself because my group hasn’t defeated the BBG that is “scheduling issues.”
Even the idiosyncrasies of the LLM being prone to being wrong works in its favor this way, as it makes it seem like a real group of players who bicker about the rules.