Modern engine control units, and transmission control units, store a massive amount of information such as boost level, fueling information and throttle position etc. If the stored values are found to be outside normal operating thresholds then the official VW Group service tool will flag this and prompt a technician to conduct further physical investigation, ie looking for unusual marks / damage around connectors, clean spots on connectors or looms in an otherwise dirty engine bay etc etc, in other words look for signs that something has been installed and removed. Any / all observations can be used by Audi / VW Group to void warranty. My advise... tuning boxes are ok, mapping is always king but you can get a decent performance boost from a box. When due a service or any warranty related works remove the box and drive the car stock for 3 to 4 days in order to "store" stock settings and flush out the "modified ones", then clean your car an especially your engine bay.
