I have the 12v but no net. 2006 S3 with Bose.
The 12v is actually useful, or at least I have found it to be.
I have in a different car used a small cool box and plugged it into the boot. Lovely cold drinks on a hot day!
I have also used it whilst travelling around to charge my drone batteries so I always have charged batteries between locations. Handy!
I've also used it to feed a phone charger cable into the rear passenger area so my daughter can entertain herself with a fully charged phone on long journeys. Peaceful!
One winter my car battery was on it's way out so I kept a jumper pack in the car in case it died totally. I topped up the charge using the 12v in the boot whilst driving.
Not everyone has a need for them, but it's there for when you do. I like that.