A moving average smooths price into a single line, making the underlying trend easier to see. The 50-day and 200-day are the most watched — when price holds above them, the trend is generally considered up.
They shine in trending markets: a rising 50-day acting as a floor on pullbacks is a classic 'trend intact' signal. Crossovers, like the 50-day crossing above the 200-day, mark shifts that many traders act on together.
They lie in choppy, sideways markets. Because a moving average is built from past prices, it lags — in a range it will whipsaw you with false signals. Know which environment you're in before you trust the line.