Playground mode opens an ephemeral copy of the notebook that isn’t saved.
Typical uses include:
- Tweaking an existing notebook without cluttering the original.
- Executing or editing a notebook shared with read-only permissions
Without playground mode, these tasks would require creating a copy of the notebook in Drive, which clutters the file list a bit. (Of couse, you can always save a copy of the notebook after opening in playground mode if needed.)