1) The broad overview of a topic
2) When I have a vague idea, it helps me narrow down the correct terminology for it
3) Providing examples of a particular category ("are there any examples of where v1 in the visual cortex develops in a disordered way?")
4) "Tell me the canonical textbooks in field X"
5) Posing math exercises
6) Free form branching--while talking about one topic, I want to shift to another that is distinct but related.
I agree they leave a lot to be desired when digging very deeply into a topic. And my biggest pet peeve is when they hallucinate fake references ("tell me papers that investigate this topic" will, for any sufficiently obscure topic, result in a bunch of very promising paper titles that are wholely invented).