Never explored it at all until recently, I told it to generate a small country tavern full of NPCs for 1st edition AD&D. It responded with a picturesque description of the tavern and 8 or 9 NPCs, a few of whom had interrelated backgrounds and little plots going on between them. This is exactly the kind of time-consuming prep that always stresses me out as DM before a game night. Then I told it to describe what happens when a raging ogre bursts in through the door. Keeping the tavern context, it told a short but detailed story of basically one round of activity following the ogre's entrance, with the previously described characters reacting in their own ways.

I think that was all it let me do without a paid account, but I was impressed enough to save this content for a future game session and will be using it again to come up with similar content when I'm short on time.

My daughter, who works for a nonprofit, says she uses ChatGPT frequently to help write grant requests. In her prompts she even tells it to ask her questions about any details it needs to know, and she says it does, and incorporates the new info to generate its output. She thinks it's a super valuable tool.