If you want to fill a limit order similar to a market order but with limits you should cross the market, not rest near it. The reason professionals might use a

If you want to fill a limit order similar to a market order but with limits you should cross the market, not rest near it. The reason professionals might use a market order even knowing about flash crashes is that there are certain positions where not filling has virtually unlimited risk regardless of fill price. Hedging option positions for instance.