Buying bargains in an uptrend. Selling back in a downtrend. Many professional traders use Fibonacci retracements at such times.

"Please let me know at 38.2% of the Fibonacci you drew."
"Alert at 50% of half price return."
“Would like to wait until we hit 61.8% at these highs and lows.”

In order to respond to such requests, I made an indicator that automatically and easily attaches alerts.