On a fresh machine, docker-pkg will build images from scratch and tag them with the version from the changelog. However the freshly build image would not match the one in the registry.
- a new image might come with different package versions
- forces us to keep all the images on the build host until they are no more needed
- if an image is not locally present, editing the Dockerfile.template without changing the changelog cause the local image to be entirely different
It seems to me it is better to be in sync with the Docker registry.