Before, runtime configuration was only available in “releases”, which is Elixir’s packaged tarball for deployments. All other configuration was compile time only. However, running your app locally in a development environment through `mix` would technically compile the app, so even though you didn’t have runtime config, it “felt” like runtime.
Because of this special feature of releases which had their own (and the only) runtime config, you often had to duplicate your config in the runtime config file and the regular compile time config file (for outside releases).
Now, with this new addition, there’s one unified place where ALL runtime config is defined, and which supports runtime config in ALL the different ways you run your app.
To me, this is a huge UX improvement for Elixir devs!