Payment of explicit interest might permit the Fed to ensure a high enough level of voluntary reserves to avoid undesirable volatility of the federal funds rate with a lower required reserve ratio or, in principle, without any reserve requirement.
This reduction is due to the forecast impact of Brexit. But the average conceals a wide range underneath. At the optimistic end, growth is predicted to reach 2.7% while, at the pessimistic end, it is predicted to be just 0.6%.