Fibonacci retracements highlight critical support and resistance levels. When a market has made a significant move, either up or down, and appears to have smoothed out at a given price level, Fibonacci levels are frequently estimated.
Traders draw horizontal lines across a chart at critical Fibonacci retracement levels of 38.2 percent, 50 percent, and 61.8 percent to highlight areas where the market may retrace before continuing the broader trend established by the first large price increase.
Fibonacci levels are extremely important when a market is approaching or has reached major price support or resistance level.
The 50% level isn't technically part of the Fibonacci number sequence, but it is included due to widespread trading experience of a market retracing nearly half of a strong move before restarting and continuing its trend.

https://en.wikipedia.org/wiki/Fibonacci_retracement