It's for people that connect their graphics card to their TV through HDMI and want the sound to come from the TV. It should bring better sound in that situation, but I don't see the point unless the TV somehow has ridiculously good speakers. Since most TV speakers are average, the improved quality of sound probably won't even be noticed.
If that's how it works, that is. It's best to have some good speakers or headphones directly connected to the sound card.