One big advantage of CUE being a total language is that you can always evaluate it in very different contexts. Yes, it doesn't matter whether your config is TC

One big advantage of CUE being a total language is that you can always evaluate it in very different contexts. Yes, it doesn't matter whether your config is TC or not if all you do with it is configure one single program. If you have an infinite loop in your configuration instance (or if you think you have, assuming you haven't solved the halting problem) you will just fix your configuration for that specific program. But large systems are not like this. There is no single configuration instance, configuration is pulled from all kinds of places, and each part of the system sees a different subset of configuration. And very importantly, this changes over time. The impact of a single change in some place becomes very hard to predict. Making the language total is one way we can limit the impact of configuration changes. Others that you mentioned are commutativity and the lack of side effects. Also, being total means you can freely evaluate CUE outside other contexts than simply program configuration. For example, you can do configuration testing independently of deployment, or you can do large scale automatic refactoring, you can inspect the system in arbitrary ways, etc.