With a market order, trades transact at the current market price. With increased high frequency trading, more and more stocks are seeing dramatic swings in prices within a short time period. Such swings add risk for market orders, as investors may get a price vastly different from what they had expected. In such cases, limit orders may be useful to minimize price risk. See article here, WSJ.
Dolvin, Steven D., "Volatility Adds Risk for Market Orders" (2015). All Chapters. 127.