I’ve used it when the topic I’m researching doesn’t lend itself to easily-searchable keywords. For example, I was trying to remember the name of low-budget smut film I saw back in the day, and the key things I remember from it – specifically, appallingly low production values, scenes being reused frame by frame multiple times throughout the movie, an actor’s atrociously bad teeth, a guy having a chauffeur but who rides around in a junker – don’t exactly work with Google searches, so I used ChatGPT. For whatever it’s worth, ChatGPT completely failed. It suggested a movie that, though I can’t find it anywhere, I’m pretty sure isn’t the right one. For whatever it’s worth, the SDMB wasn’t much help, either.
I also asked ChatGPT about a book I remember from my childhood, of which I have only vague memories, and it admitted defeat rather than making something up, so that’s encouraging.