It allows OEM's to install a codec, normally used for "onboard" devices, into a slot card, with no additional hardware. In other words, it's for adding the worst, cheapest hardware. And because there isn't much demand in the retail market, if you find a card to fit it, that card will probably cost as much as a much better PCI card.
<font color=blue>Watts mean squat if you don't have quality!</font color=blue>