It turns out to be absurdly useful, to a very un-intuitive degree.
One trick I use is to assume it has a "Wikipedia-level" knowledge of pretty much any topic. Often that's what I need! I want to ask some quick questions of someone eloquent who's read the Wikipedia article about something, to save me from having to read the whole thing myself.
If I need more expertise than you can get from reading Wikipedia I know that ChatGPT alone is very unlikely to cut it.