WHY do we need to Manage Non-Conformance?
If there is not full and clear identification, management and documentation of non-conformities then there is no way of knowing whether the facility, product, software or service that is the output of the project enterprise is fit for purpose.
Not only would there be an ill-defined risk of failure when used, it would not be possible to make accurate plans for maintenance, testing and possible replacement.
There is also the risk that non-conformance discovered during quality verification exercises or commissioning - before operation of the facility - might stop project progress for a long time, or even indefinitely.