Under such circumstances, for Friedman, two motives exist for a consumer unit to spend more or less on consumption than its income: The first is to smooth its consumption expenditures through appropriate timing of borrowing and lending; and the second is either to realize interest earnings on deposits if the relevant rate of interest is positive, or to benefit from borrowing if the interest rate is negative.
Under such circumstances, Friedman identifies two reasons why a consumer unit might spend more or less than its income:  The first reason is to manage spending by timing borrowing and lending effectively; the second reason is either to earn interest on deposits if the interest rate is positive or to benefit from borrowing if the interest rate is negative.