Let's review businesses whom release press releases in practice. Great example is Microsoft. Of course your not Bill Gates and you don't have windows but your a business who can learn form other successful businesses. Recently Windows OS 8 preview was posted all over their website and utube. Windows displayed and gave their brand loyal clients a peak at the new product which will generate "fill the need" within their clients minds. The client sees the new product and wants it. However, they have to wait until its official release to make the purchase. So in the mean time, they have some time to save up for the release so they can purchase it. So as stated above it's a marketing tool and generates the mental idea of "fill the need" inside your clients head. In limens terms is just "Hype". But hype sells products and creates sales.