Is decanting a red wine necessary to improve the flavor? - Quora

The reason for decanting red wine relies on the chemical reactions taking place during aging. These reactions are in the reductive category which is the absence of or very limited exposure to oxygen (indeed though corks breath, they allow very little I mean VERY little oxygen into the wine). In this state a lot of the aromatic compounds in wine as ... See more

The rule of thumb would be: if the wine would improve in the bottle for a few years, it will most likely improve in the decanter.