Not everyone in the car wants to hear the same things at the same time. Children don’t necessarily like the same music as their parents. Drivers and passengers don't always want to listen at the same volume. And it’s frustrating for everyone when a phone call comes in and the music stops, or navigation prompts interrupt the best part of the song.
A car should be able to play different sounds in different seats according to what makes sense for the person sitting there – so the journey becomes a personal experience for everyone in the vehicle.