The central bank could increase or reduce people's bank balances as they see fit, central governments could tax transactions as they occur, and illegal activities (that aren't state approved) could be prevented. Furthermore, in an all-electronic system, enemies of the state could theoretically be frozen out of the entire world economy.

Fortunately for humankind, the War on Cash is a pipe dream, like the War on Drugs, the War on Terror, or any other war on a concept. Physical money cannot be killed, and just like drug cartels or terrorist groups, trying to kill cash will only make it stronger. The world's black market, it turns out, is larger than the economy of all but the richest few countries, and all those flying the black market's pirate flag will need a means of exchange. Whatever this currency ends up being, it will not be controlled by government employees, and it will likely resemble ancient means of exchange: precious metal coins.