I find it particularly useful for configurations that often have repeated boilerplate, like ansible playbooks or deploying a bunch of "similar-but" services to kubernetes (with https://tanka.dev).
Dhall is also quite interesting, with some tradeoffs: https://dhall-lang.org/
A few years ago I did a small comparison by re-implementing one of my simpler ansible playbooks: https://github.com/retzkek/ansible-dhall-jsonnet
The whole point of the parent is that JSON is the Pareto solution, which I agree with.
But it does grind my gear.
It's configuration with a build step. Which is an option, but that's pretty different than JSON, YAML, TOML, etc.
