The purpose of Market Forecasting is to determine, with a high degree of accuracy, when the market is likely to start a new leg up or down. In other words, the plan is to 'when' the market is likely going to make a new top or bottom.
Now why is that important?
Trading is all about probabilities and risk. You first determine the probability for the direction of the market, and then you must determine the risk exposure if you were to take the trade.
What Market Forecasting attempts to do is to find the right time to enter the market where the risk exposure is as low as possible while the profit potential justifies the risk.