Greg Mankiw makes a good point about the investment tax credit

An investment tax credit is probably less effective when interest rates are very low, as they are now, than in normal times. As Greg Mankiw explains:

However, the impact will be relatively modest. Notice that expensing merely accelerates deductions. Thus, the value to the firm depends on interest rates. With interest rates near zero, the impetus to investment is small. Put another way, this policy can be seen as giving firms a zero-interest loan if they invest in equipment. But with interest rates near zero anyway, the value of the loan is not that great.