This is when you are not sure in which direction the price will go in the near future and want to insure, you simultaneously open deals for purchase and sale. That is you set up a "lock" to close all the possible ways of retreat rates. Regardless of what direction the graph moves, you'll be in the black. But we must understand that in exactly the same way you will be in the red on its opposite transaction. Therefore it is better to close one of the deals as quickly as possible when profitability is certain in the second deal.