Lets say you have a stock like GROW or HANS - a real crazy stock that could easily go up 100% or down 50%. You don't want to predict, so you just buy both the calls and the puts expecting a big move in either direction. One contract will probably expire worthless and the other will be in the money big. You lose if the volume and volitility dries up and the stock goes nowhere and the profit on one contract isn't enough to cover the loss on the other.