If they are jumping in and out of the market, they merely generate trading activity. That makes it harder for one player to manipulate the market. There are stock markets, for example in some Middle Eastern countries, where trading is …

Crude oil spot and futures markets
Much of the price discovery in stock markets happens in the index futures market. Individual stocks are priced taking the broader market index as given. If the index has fallen 5% on a day and a specific stock has not traded so far, …

Much of the price discovery in stock markets happens in the index futures market. Individual stocks are priced taking the broader market index as given. If the index has fallen 5% on a day and a specific stock has not traded so far, …