CFOs invariably ask themselves two related questions when managing their balance sheets: should they return excess cash to shareholders or invest it and should they finance new projects by adding debt or drawing on equity? Indeed, achieving the right capital structure the composition of debt and equity that a company uses to finance its operations and strategic investments has long vexed academics and practitioners alike.¹ Some focus on the theoretical tax benefit of debt, since interest expenses are often tax deductible. More recently, executives of public companies have wondered if they, like some private equity firms, should use debt to increase their returns. Meanwhile, many companies are holding substantial amounts of cash and deliberating on what to do with it.

The issue is more nuanced than some pundits suggest. In theory, it may be possible to reduce capital structure to a financial calculation to get the most tax benefits by favoring debt, for example, or to boost earnings per share superficially through share buybacks. The result, however, may not be consistent with a company's business strategy, particularly if executives add too much debt.² In the 1990s, for example, many telecommunications companies financed the acquisition of third-generation (3G) licenses...