On August 24, many stocks fell by large percentages, only to recover shortly thereafter. Investors with standing stop-loss orders likely didn't fair well. And, in fact, many are blaming these orders for the volatility. The NYSE plans to eliminate stop orders, but brokerage firms can still facilitate these for their customers, as long as the final order is sent at market. See article here, Bloomberg.
Dolvin, Steven D., "NYSE to Stop "Stop Orders"" (2015). All Chapters. 145.