ACC (together with DSG) is active at speeds from 0 to 210 km/h, with cruise control starting at 30 km/h. As sketched here, predictive speed control provides more comfort and convenience. At the same time, predictive braking and accelerating functions can also help to lower fuel consumption.
The important point here is that ACC with predictive speed control supports drivers within the system limits, but drivers retain control of their cars at all times and are therefore responsible for their cars in every situation. Drivers can always “override” this semi-automatic system by turning it off, braking, or accelerating.