Postgres provides a robust and flexible permissions model for users to manage access to their data. The model is based on roles, privileges, and objects, but has subtleties that must be understood by database administrators to create airtight access. Roles can inherit permissions from other roles they are a member of, including the public role, which every other role is implicitly a member of. The public role provides common privileges such as connect, temporary, execute, and usage, but its privileges can be revoked. Superuser roles are all-powerful and bypass privilege checks, and should be used with care. Grant commands only grant privileges on existing objects, and default privileges control the privileges granted to new objects created in the future. Understanding these concepts is crucial for managing and protecting Postgres databases effectively.