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My understanding is that the only thing yeast really "does" in life with the energy it extracts from sugars is multiply. In the process, it converts the sugars to waste products (from the yeast's point of view). Those waste products differ when the yeast has O2 versus when it does not.

If yeast is working aerobically (in the presence of O2), it can extract roughly 18x as much energy from a sugar molecule as it can when working anaerobically (no O2). Thus it should be able to multiply a lot faster when O2 is present, because the metabolic pathway it can use then is so much more efficient. However, the cost of this is that the sugar it consumes aerobically is converted to CO2 and water, rather than CO2 and alcohol. So basically by aerating you will be accelerating the initial multiplication of the yeast at the cost of slightly more water and less alcohol in the final product.

There is also the issue of what oxidization does to the flavor of the wine. Oxygen is an extremely corrosive element that reacts with just about anything, including many of the flavonoids, etc., in the must. To much O2 exposure will lead to a substantial difference in the flavor of the wine. Whether you think it makes it better or worse is a matter of your own personal preference. (The experts will say it makes it worse, but do you drink wine based on what other people tell you they like, or what you like? :-)

Kevin