Neither a weather forecast, nor an economic forecast needs to be 100% accurate to be useful. I find that the weather forecasts I get are useful. It doesn't matter if the rain comes in the morning, like it said, or if it turns out to happen in the afternoon; I need my raincoat either way. When I am planting my garden, I don't need to know whether it will sunny or cloudy, just so long as it doesn't rain or be too windy that day. People found weather forecasts to be useful enough to publish many years ago, before they were even a tiny bit as accurate as they are now.
While managing an economy is certainly more complicated, I certainly don't think anyone is going to be planning it down to the last kg of rice or pair of pants. There will be surpluses, stockpiles and waste, of course. But more powerful predictive tools can help us reduce waste, even out the bumps in the market and generally reducing shocks. The market is powerful, but it can benefit from measures to reign in its excesses. Predictive tools can help that.