VCDS is quite a powerful tool, there are many 'basic' settings that can be changed that alter the way the van behaves/performs but it can also be used to activate or add additional options and features for example I have added a rear view camera and front parking sensors, after physically installing them you have to make a few programming changes to tell the van the additional parts are there so it looks for them and communicates with them
That's one side of it the other is the ability to read and reset fault codes if ever your engine management light comes on, not so important if your under warranty but if your are not dealers will charge £50-75 just to plug a laptop in and read a fault code that may or may not be an issue
The other thing it can do is read detailed engine and operating info, you can run the van with it connected and view live data engine characteristics throttle position etc etc prob not used by many but things like this help build info for the community on things like pressures, temperatures, dpf info and the like
A lot of these things lots of people will never use but if you only use it to read a fault code a few times it's all but paid for itself and if it helps you fix something at home instead of paying a dealer to do it then you can potentially save big time but it's all down to individual ability, understanding and confidence in talking things on so holds different value to different people I suppose