To provide a real-life use-case for such a tiny container image: With Kubernetes one may want to run the service container as a random or at least non-root user id and store data in an attached volume. That volume will usually be attached as owned by root. So often an init-container is used, which runs once, before the service container is started, to change the permissions.

Here is an image with a statically linked chown binary from the busybox tools cowering this use case: https://hub.docker.com/r/privatebin/chown (I am the author of that image)

Benefits of using a small image are less attack surface and faster operation (less data to download, lower startup time, less memory, etc.).