Sometimes an application will start out with a need for just a configuration format, but over time you end up with many many similar stanzas, and you would like to share parts between them, and abstract some repetition away. This tends to happen in for example Kubernetes and GitHub Actions. When the configuration language does not support abstraction, people often reach for templating, which is a bad idea for the reasons explained earlier. Proper programming languages, possibly domain-specific ones, are a better fit. Some of my favorites are Nix and Python: