Explanation
If your organization is small, or if you are still in the proof-of-concept stage of evaluating OracleCloud Infrastructure, consider placing all of your resources in the root compartment (tenancy). This approach makes it easy for you to quickly view and manage all your resources. You can still write policies and create groups to restrict permissions on specific resources to only the users who need access.If you plan to maintain all your resources in the root compartment, we recommend setting up aseparate sandbox compartment to give users a dedicated space to try out features. In the sandbox compartment, you can grant users permissions to create and manage resources, whilemaintaining stricter permissions on the resources in your tenancy (root) compartment.
https://www.oracle.com/a/ocom/docs/best-practices-for-iam-on-oci.pdf