Why decant? For older wines, to remove any sediment, which beside being unsightly can taste bitter. Most younger red wines, and even some white wines, will benefit from the additional aeration of being poured into a decanter some while before serving. An hour or so in a proper decanter will soften the tannins of Cabernet Sauvignons, Bordeaux and many Italian reds and allow them to improve in aroma and flavor as volatile aromatics are released. The same is true for full-bodied white wines. Vintage Ports almost demand a few to several hours of "breathing" in a decanter. Of course, a fine crystal decanter makes for a far more presentation at the table, especially when engraved with your brand.