The practical problems of social planning

Currently, some central banks have started to act as social planners to help the financial industry to locate the resources. As explained in textbooks, we know that the output of a social planner is efficient and the best of a free market can achieve is the level of the social planner output. However, in reality, what a social planner produces is not necessary to be efficient. The best example is the Soviet. In reality, central banks can never get all information they need. The finance companies may lie about their true preferences, the cost to ensure they tell truthfully is expensive. Moreover, the red tapes could worsen the problem of inefficiency, especially when a central bank starts to play a larger part in the economy. Therefore, I deeply doubt about the efficiency of central banks in helping locate resources.