In role-based access control, each role carries a defined set of permissions, and users receive the roles that match their job. A reviewer role might approve work but not change firm settings, and a client role might see only its own documents.
RBAC makes permissions understandable and auditable. When someone changes jobs, their role changes and their access follows. Fine-grained systems combine roles with assignments, so a preparer sees only the engagements assigned to them, which further applies the principle of least privilege.