Enforces the concept of least privilege. Granting users business functionality doesn‘t imply entitlements may be used at any time. For example a bank teller shouldn’t withdrawal money from customer accounts outside of normal business hours or freelance contractors don't require access to production resources to do their jobs.
Enables Regulatory Compliance. Who has been granted authority to the most important resources? How can we be certain that terminiated employees and customers no longer have access to controlled resources?
Enforces separation of duty policies. For example traders must not be regulators or purchasing agents cannot approve transactions.
Eases administration costs due to elimination of redundant resources. Enable business units to be delegated administrative tasks.