…, the Fed must stop providing incentives for banks to keep money out of the economy. Since 2008, the Fed has been paying financial institutions interest on excess reserves parked at the central bank — reserves that have grown to an unprecedented $2.4 trillion. That is insane. Instead of paying banks interest on these reserves, the Fed should charge them a fee that would be used to provide direct loans to small businesses.
The banks don't really decide how much reserves they have. The Fed controls the level of reserves by buying and selling Treasuries and other securities. (That's how reserves got so big in the first place.) So, no risk of hoarding.
Reserves are deposits banks have at the Federal Reserve; some are required by law to be held against checking deposits, but banks also hold reserves at the Fed in excess of requirements. Importantly, the amount of Fed deposits held by the banking system as a whole is determined by Federal Reserve open market operations, not by the banks themselves.
イングランド銀行季報の"Money creation in the modern economy"での説明。
A related misconception is that banks can lend out their reserves. Reserves can only be lent between banks, since consumers do not have access to reserves accounts at the Bank of England.