Not who you're responding to, but I used one extensively in a recent work project. It was a matter of necessity, as I didn't know how to word my question in the technical terms specific to the product, and it was something that was just perfect for search engines to go "I think you actually mean this completely different thing". There was also a looming deadline.

Being able to search using natural language, especially when you know conceptually what you're lookong for but not the product or system specific technical term, is useful.

Being able to get disparate information that is related to your issue but spread across multiple pages of documentation in one spot is good too.

But detailed references on code? Reliable sources?

I have extensive technical background. I had a middling amount of background in the systems of this project, but no experience with the specific aspects this project touched. I had to double check every answer it gave me due to how critical what I was working on was.

Every single response I got had a significant error, oversight, or massive concealed footgun. Some were resolved by further prompting. Most were resolved by me using my own knowledge to work from what it gave me back to things I could search on my own, and then find ways to non-destructively confirm the information or poke around in it myself.

Maybe I didn't prompt it right. Maybe the LLM I used wasn't the best choice for my needs.

But I find the attitude of singing praises without massive fucking warnings and caveats to be highly dangerous.