Net Income approach says that a raise in the proportion of debt financing in capital structure results in an increase in the proportion of a cheaper source of funds. This in turn results in diminishes in overall cost of capital leading to an increase in the value of the firm. The major reasons are:
-  The assumption of cost of debt to be fewer than the cost of equity.
 
-  The interest on debt is a deductible expenditure when the company gets the tax benefits on it.