The firm must earn a minimum of rate of return in order to cover the cost of generating funds to finance investments. If this is not the case then no one will be willing to buy the firm's bonds, preferred stock, and common stock. The firm's required rate of return, is called the COST OF CAPITAL. or the hurdle rate. The cost of capital is the required rate of return that a firm must achieve in order to cover the cost of generating funds in the marketplace. This is why Howard Sloan wants to estimate the firm's hurdle rate
When there are differences in the degree of risk between the firm and its divisions then it is not justifiable to use the firm's weighted average cost of capital as the divisional cost of capital.
We use the company's cost of capital to value new assets which have the same risk as the old ones. If the company is acquiring new assets whose risk is more or less than the risk of the existing assets then the capital required to finance(fund) the new assets will have a different cost of capital as investors demand a return based on the risk to their investment.