I have plenty of cases with yaml where I care about the formatting of the serialized output. I have to use obscure hooks into pyyaml's inner workings to tweak things just right. In some cases, I end up having to do some of the serialization myself. While technically it doesn't matter because it's all equivalent once in memory, there are externalized costs once you're integrated into a large system. The whole point of using something like yaml or toml is to be human friendly.