Surfactant is like oil. Oil helps to lubricate the pistons in a car, which reduces friction, so the pistons can move easy. Surfactant, does the same thing. It helps to lubricate the lungs and thoracic cavity, so the lungs can expand and collapse more easily, which allows us to breath easier.
Now, if their is a decrease in surfactant, patient will have trouble breathing, an increase in breathing, and in some cases, the reduction of the surfactant can cause a pneumothorax.