Visceral pleura is a covering of the lungs. The word pleura always refers to the lung and visceral means the covering of an organ. If you have pleuritis, for example, you have inflammation of the pleura in the lungs.
If your lungs were lacking visceral pleura, they would not be working very well, if at all. The pleura helps to reduce the friction of breathing, the many inhalations and exhalations, the wear and tear. It makes breathing easier by having this lubricating action. Without this physiological response, the lungs would soon "dry up" and be unable to continue to function as exchange agents for oxygen and carbon dioxide.