It makes your desktop look pretty
Instead of having a nice transparent themed computer it will look some what like a remixed theme for Windows XP (still bubble themed but silver/grey), and you still can use the Legacy Windows/Classic look of Windows 2000.
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Vista for you should look like this, I've taken these pics myself from my older computer that doesn't fit areo requirments. I will post some newer pics of my current PC that has areo enabled latter.