It's just that from my regulatory perspective, if an excel spread sheet is used to compute W&B calculations, the failure of the software won't result in a catastrophic event IAW FAA FAR25,27,23 etc..1309 System Safety Assessment. By catastrophic I mean the loss of aircraft and life. However it is the unannounced misleading or incorrect information provided by the excel W&B calculations that can have aircraft level implications.
So if the crew insert the wrong take-off weight and speeds into the Flight Management System, from such erroneous calculations, the aircraft may not be able to take off in time...
Quite the tricky topic indeed.