C2422HE P2424HEB, Windows playback shows two

With these monitors, when I go into the control panel, sound, playback, there are two sound output options I can select, and I just wondered why this was the case? 

For example: (on C2422HE)

Echo cancelling speakerphone (this one allows louder volume and maybe better quality)

Dell C2422HE

Is there  a reason for this? And a clever way to use the second?