[benguillet]

One use case I see is if you're using Nix for all your local development, but Docker in production (because it's the easiest these days: package an image, give it to ECS/Fargate or equivalent and it's good to go).

You're not using Docker in development because of the sync issues on Mac between the host and the containers, but ideally you still want as much as possible the development and production environment parity (same versions of dependencies, etc). You can build your Docker images with Nix to ensure the dependencies versions you're developing with will be the same in prod.