CWS had it's uses in earlier generation aircraft such as the A300-B4, which did not have a Mach Hold. CWS was useful to periodically adjust pitch attitude to maintain the desired Mach Number.
Other than that, on more modern types with almost every mode controllable through a basic or more advanced mode, I can't think of much use for it. If I had it, (maybe I do) I doubt that I could think of much practical application for it.
Useful in it's time, a bit out-moded now
Regards,
Old Smokey