Monetary policy transmission: Another significant reason for the importance of Payment Systems is the role they play in efficiently transmitting monetary policy signals to the markets and economy as a whole. The monetary policy actions of the central bank influence either the quantity of money (i.e. money supply) or the price of money (i.e. interest rates at the short-end of the curve).
Both these measures require a reliable large-value payment system with same-day (preferably real-time as is the norm) settlement. The effectiveness of any monetary policy measure depends to a large extent on the efficacy and soundness of the large-value payment system.