It depends. They can help prevent "artificial" crashes caused by liquidity issues and/or algo-driven feedback loops, and, maybe, to some extent, FOMO feedback l

It depends. They can help prevent "artificial" crashes caused by liquidity issues and/or algo-driven feedback loops, and, maybe, to some extent, FOMO feedback loops (everyone is selling so I should too!). If there is sudden mass sell-off, the buy side of the order book can run thin. The order book is supposed to be a representation of people's intentions to buy or sell, but it's no a true representation because people don't necessarily bother putting in limit orders far away from the current price. The halt gives time for people to put in their buy orders and put some back-pressure on the sell-off. It also gives time for traders to tweak or turn off their algos if they are behaving badly. If the crash is a "true" crash caused by fundamentals, in other words the economy is going to shit, I don't see how halting can help much.