For still wine
After opening, most wine bottles will last up to 3 days (if stored properly in a cool and dark place) maintaining some semblance of drinkability. But to maximize that fresh taste, one needs to minimize the amount of oxygen exposure in the bottle. Extended exposure to oxygen will turn the wine bad faster than a Jo Koy joke does to a room full of Pinoys who've heard Rex Naverrete jokes before.
Using a wine pump in-between pours can help retain the freshness and extend the drinkability of a wine for a total of 4-6 days. If you like to enjoy a glass a night for yourself and don't want to worry about not being able to finish the rest before it goes bad - this tool is for you.
The stoppers basically replace the cork/screwcap. When you're ready to put away the wine for the time being, just pop in the stopper, and give it a few vigorous pumps with the pump until you feel the air nearly sucked out of the bottle.