 Spreads are either "bought" or "sold" depending on whether the trade will profit from the widening or narrowing of the spread.The volatility of the spread is typically much lower than the volatility of the individual legs, since a change in the market fundamentals of a commodity will tend to affect both legs similarly.The margin requirement for a futures spread trade is therefore usually less than the sum of the margin requirements for the two individual futures contracts, and sometimes even less than the requirement for one contract.