Banks are required by law to hold a certain fraction of their deposits in reserve accounts at the Fed, but receive no interest on these deposits. Having the authority to pay interest would solve two technical headaches for the Fed. If they earned interest from the Fed, banks would have no incentive to lend out excess reserves for less. That would make the Fed’s benchmark federal-funds rate, which banks charge on overnight loans to each other, less likely to plunge below the Fed’s official target — now 2% — on days when the banking system was awash in cash. In addition, the Fed could theoretically combat the credit crunch by buying securities or extending loans without limit without causing the federal-funds rate to fall to zero, something that could fuel inflation or distort markets.
In other words, the concerns were that banks would hold too few reserves and that we would end up with higher inflation. But today’s concerns seem to be that banks are holding onto too many reserves and that we may be in for a deflationary spiral and inadequate aggregate demand.
This post also noted that Congress originally intended for interest to be paid on reserves starting in 2011 out of concern that the government might lose income to private banks. While pumping a few extra millions of dollars into the private sector right now might be good Keynesian economics, perhaps delaying this new policy until 2011 would have been better given the collapse of the money multiplier.