How can restrictive covenants in bonds be both an agency cost of debt and a way to

Question:

How can restrictive covenants in bonds be both an agency and a way to prevent agency costs of debt?
Cost Of Debt
The cost of debt is the effective interest rate a company pays on its debts. It’s the cost of debt, such as bonds and loans, among others. The cost of debt often refers to before-tax cost of debt, which is the company's cost of debt before taking...