In the above example the pub_release project is dependant on dcli.
As I'm also the developer of dcli I often make changes to dcli to support pub_release features.
I find it easier to make dcli changes and test them in pub_release before I publish dcli to pub.dev.
The dependency_override allows me to work on both code bases simultaneous.
Publishing
When it comes time to publish my package I need to remove the dependency_overrides as pub.dev only allows you to have dependencies on other published packages.
pub_release supports dependency_overrides by automatically removing them during the release process.
Once the package has been published it restores the original overrides.
Multi-package releases
The support of dependency_overrides is particularly important when doing multi-package releases as it is normally to have overrides for each of the related packages.