Why is it necessary to separate the management function in an organization from those of finance and residual claimancy?

Separation of the management function from those of finance and residual claimancy is essential because:
a) The skills and opportunity costs of management is entirely different from that of the residual claimants.
b) Residual claimants who have interests in more than one firm are diversified in ways that managers who depend on a single employer for most of their incomes cannot be.
c) A diversified residual claimant generally has less understanding of the firm than a manager and has little knowledge that is likely to improve the quality of the manager's choices.