You have asked a question which was a hot research topic during early 70s. however, it will remain a research topic for the future also.

Debt and equity financing have a direct effect on a firm's WACC, which is set on by its capital structure. A lower WACC enhances valuation and lowers financing expenses. Investment projects are evaluated using net present value (NPV); a positive NPV is in line with financial objectives and increases shareholder wealth.