What use cases involving curl will benefit by using http3?
Anything that involves high latency and/or packet loss. And in general: testing servers.
The question is also a bit odd, to be honest. There's no need to look for a beneficial use case to add support for the next iteration of the HTTP protocol.
Testing your http/3 endpoint
it’s… curl, it’s supposed to do all the networking protocol things
It will be able to speak http3.
So what were the dangers with QUIC protocol again? That the big-tech would control the market?