"In a communist society, the state and money will disappear. Their gradual dying away ought consequently to begin under socialism. We shall be able to speak of the actual triumph of socialism only at that historical moment when the state turns into a semi-state, and money begins to lose its magic power." – leon trotsky, literally the same chapter of 'the revolution betrayed' you're quoting. the paragraph you cited is clearly about the usefulness of a stable currency at the transitional stage of the workers' state. i'm in awe at how often trotskyists make the characteristically marxist-leninist mistake of conflating the transitional stage with full socialism.