An in-charge auditor is drafting interim tests of controls for the American Optical Company, a December 31 year end optics manufacturer located in Southbridge, Massachusetts.

Tests will be performed in mid-September, engage three staff for two weeks each, and, assuming the audit team's tolerable rates of deviation exceed the estimated population rates of deviation, will likely drive the engagement partner to assess control risk below the maximum.

Required: 

Why bother? Why not simply perform substantive tests of financial statement account balances and disclosures at year end? After all, the firm's opinion will say everything about the financial statements, and nothing about control risk.
Discuss.