You could have your iPhone docked in some kind of stereo system and have bazillion gigabytes of music that don't fit on iPhone, or just don't want to get up to

You could have your iPhone docked in some kind of stereo system and have bazillion gigabytes of music that don't fit on iPhone, or just don't want to get up to change the music. I don't think it's used to stream to iOS devices so they can play it back trough their speaker or headphones - I guess it's to use their line out.