I'd use a "subpar" LLM for any coding practice where I want to do the bulk of the thinking and where I care about how much coal I'm burning.

It's kind-of like asking, for which kind of road-trip would you use a Corolla hatchback instead of a Jeep Grand Wagoneer? For me the answer would be "almost all of them", but for others that might not be the case.

The kind of coding that happens after the internet goes down. How important of a use case that is depends heavily on why the internet went down.

A LLM that I don’t host is a non-starter, so even a “subpar LLM” is better than someone’s cloud.