Postgres Row Level Security (RLS) is a feature that allows security policies to be embedded at the database level, ensuring consistent application regardless of how data is accessed. RLS alone has limitations, such as coarse-grained control and potential security vulnerabilities. Combining RLS with an application-level authorization service like Permit.io can create a comprehensive security solution, providing fine-grained control, centralized policy management, and real-time policy updates across multiple systems.