And to be fair, ChatGPT warned me about all of the potential issues with indexes. I did actually evaluate its suggestions and decided they were probably going to be worth the potential cost; and as I've said in a sibling thread, it was just a local SQLite database that consisted of data slurped from another source; so even if I'd somehow screwed the whole thing up, I could just delete it and start over.
Lesser issues: additional strain on index rebuilding whenever that happens; messing with execution plans and causing the query planner to be inefficient; primary/secondary memory overhead; or if your DB engine uses locks you can run into a myriad of issues there.
I'm all for SWEs learning about databases, as I'm morally opposed to the proliferation of ORMs and the like, but I don't think ChatGPT is the right way to go about things long-term. It's similar to Googling or using StackOverflow: yes, you will find information that is relevant to what interests you at the moment, but it's soon forgotten and does nothing to help build long-term mental models.