Sucking air out of a partially-consumed bottle of wine is simple functionality that will help preserve leftover wine for use another night.
Air: good for us, bad for wine
Fine wine and oxygen don’t mix. Prolonged exposure to oxygen will cause wine to oxidize, breaking down the aromatic phenols which gives wine its distinct bouquet and taste, and changing its sensory characteristics. Unless it’s a bottle of Madeira, these changes usually aren’t good. The bouquet can smell a little cooked or raisiny, the taste is flat or a little off, often masking the true flavor of the wine, and the color may have turned brown. While you can still drink this wine and it won’t harm you, it probably won’t be a pleasant experience. Don’t pour that wine down the drain. While it may not be good for drinking, it can still be used for cooking.
Less Air = Less Oxidation
Vacuum and pump systems work by removing most of the air from an open bottle of wine and slowing down the oxidation process. Sticking a cork or bottle stopper in the wine and putting it into a refrigerator may keep it from tasting off for another day, but using a wine pump system can preserve it up to a week. When drinking wine: