For C++ developers, more cores to build on means faster builds. If your project is big, more cores can make a significant boost. If you have a local k8 cluster with spare CPU, it's amazingly simple to turn it into a build-machine.
Some times it's required to copy a docker container between machines, or even developers. One option is to use a hosted repository and pay some money for this opportunity. Another option is to use a machine that has a reachable IP address and Docker to run a private and secure Docker Registry.
Building something in Jenkins, using a declarative pipeline and deploying it to a Docker container is common, and you would expect it to be well documented and trivial to do right? Well, it is now.