A more passive role and limited concern with agency costs might be sufficient for a company doing well in business and run by an effective management team.
Agency costs mainly arise due to contracting costs and the divergence of control, separation of ownership and control and the different objectives (rather than shareholder maximization) the managers.
The principal-agent view of credit markets refers to the costs (agency costs) associated with borrowing and lending due to imperfect and asymmetric information between lenders (principals) and borrowers (agents).