The pre-production inspection can also focus on the processes followed as production starts. Sometimes this can also be critical, many factories very often cut corners and do not respect the blueprints (e.g. patterns for cutting fabric are received from the buyer, and they are modified to make the process easier and faster).
It usually takes place once some finished products have come out of the lines. If quality issues are found, what is already produced might be re-workable, and corrective actions can be taken for the rest of the job. It gives time to plan ahead, and even to avoid delays (repairs and re-inspections take much more time when problems are noticed after all production is finished).
Its objective is really to confirm a shipment’s quality, rather than catching issues early. Therefore we usually advise our clients to complement final inspections with a DUPRO, to avoid finding disasters at the last minute.