What does `docker system prune -a` actually do?

Question

My empty space before running docker system prune -a was 900 MB and running it gives me 65 GB free space although the command report that it cleaned only 14.5 GB

Is the report is just wrong on am I missing something here?

The docs is not telling something new and it would be normal if it clears only 14.5 GB and this only gives me one answer that I'm doing it in a wrong way. Any thoughts here?

Answer 1

This will remove following content form your host machine where docker is running

    - all stopped containers
    - all networks not used by at least one container
    - all images without at least one container associated to them
    - all build cache