Decanting is a process used to allow the sediment in aged wines to settle down.
The practice dates back to Ancient Rome. Even then, they used glass decanters, not very different from the ones we use today. However, the contemporary decanters have stoppers which we can use to control how much aeration we would like. These stoppers date back to decanters made by the British in the eighteenth century.
Decanting is a process that is largely associated with red wines.
You don’t really need to decant a white wine, unless it is recommended otherwise.
Red wines, especially those that are ten years old or older, have much more sediment. The sediment has to be segregated and it cannot happen in the wine bottle. White wine does not have this sediment problem even if you go for some of the oldest and rarest white wines. The fermentation process is different, the grapes are of different varieties and white wine is much less opaque. There are some white wines that are almost transparent. You would easily get to know if there is sediment. This does not happen with any red wine.
While you don’t need to decant a white wine, you should always consider it if you are buying a cheap variety. You may have tasted some inexpensive wines brought from a grocery store. These wines often smell like rotten eggs. This smell is basically sulfur dioxide. The moment you open a cheap bottle of wine, you would get this smell and it can ruin the whole wining experience. You can open such a bottle, pour the wine into a decanter and let it be for a few minutes. If the smell is still prevalent, swirl the decanter and let some more air into the vessel. The strong smell will be gone soon enough.
The same can be done with a white wine that has some unpleasant smell.
There are white wines that are excessively tart. Their acidic tone can be discomforting for some people. Pinot noir has some really acidic varieties. You can always use a decanter to let such wines sit for a while. The process will smoothen the flavor of the white wine and you would have a much more satiating wining experience. You must be sure a particular white wine and whether or not it needs to be decanted. Some white wines will actually taste bad if you decant them.