The swing highs and lows that the Zig Zag indicator identifies may represent future support or resistance levels. It can, therefore, help traders spot key price levels that may be control points for future trading.
The Zig Zag sometimes reveals a major trend change by virtue of the lines it draws marking out a well-known market reversal chart pattern such as the head and shoulders pattern. Traders still need to augment such indications from the Zig Zag with traditional price action analysis, using technical indicators such as moving averages or candlestick patterns.
The important thing to keep in mind is the limited and specific purpose of the Zig Zag indicator. Its purpose is to filter out small, insignificant price fluctuations so that a trader looking at a chart can maintain their focus on the overall trend. For pinpointing trade entry and exit points, traders are better served by more traditional technical indicators applied to price action.