There are two schools of thought on aeration. The first applies to old wines where aeration allows the wine to come out of what we call an anaerobic funk from all the oxygen being used up in aging reactions thus leaving the wine in what we know as a reductive (opposite of oxidative) state. The second some people utilize on young tannic wines to help open a wine’s aroma up and it can soften a wine as well. This process is to counter the strong tannins in the wine by trying to speed up the aging process.
I’m a purist when it comes to aeration and prescribe in the first reason but not the second. When decanting an old wine (see Wine Knows –decanting) the practice of aeration can be accomplished in two ways. When pouring the wine from the bottle into the decanter you can hold the bottle above the decanter and let it splash into the new container, thus adding oxygen. In really old wines you need to be careful as this could cause them to go past the point of the oxidation you are seeking. The alternate technique for handling these old wines is to time the decanting so that it has time to gently absorb air. This could be anywhere from one to two hours in advance of serving, without splashing, and then let the wine sit without a cork or stopper to breath. A reduced wine has a stink to it. A second outcome of bottle aging is what we call bottle bouquet which is sort of a musky cellar floor nose in the wine. This gentle type of aeration will often times reduce these musky notes and let the fruit show through.
Those that want to force aging on a wine I say why don’t you wait until the wine ages as it was intended to and then decant it. To use one of these aeration devices that add air to a young wine not only blows off the more delicate fruit and spice aromas that you could be enjoying but these devices beat up the wine and cause subtle oxidative qualities known as bruising.