Does this software allow you to actually make changes to the car or does it simply produce a report which allows you to see where there are problems with the engine?
While I think the idea of messing around with my cars ECU sounds like fun, I also feel its probably the fastest way for me to completely

my car up.
You can change settings, most common of which are comfort settings but how many you can change depends on your vehicle. For instance, on a
Mk4 Ibiza you can only change things like auto-locking, 1 touch unlocking etc, whereas on a 2009 Audi A6 you can change a hell of a lot more.
You can also change engine settings, such as increasing idle speed, reduce EGR usage or even disable it altogether, as well as other things.
Use common sense with the program and you won't **** things up, I was once a learner with VCDS and have been using it for about 3 years now yet have never managed to brick an ECU.