This check is conducted during the very early stages of the production process (between 0 and 20%). The purpose of the check is to inspect the process parameters and to verify that the final product will meet the desired quality requirements.
We are humans and naturally humans make mistakes, so do factories in China. About half of the factories in China have production issues. If no strict quality check is performed, factories will make according to their standard. That is why to determine the faults earlier is a time and cost saving process,when you figure out the problems when all goods are finished, it will waste lots of time and money to revise. In our experience, we did a quality control while the production just had started, we figured out the color the factory used was totally different from what the customer wanted. This is a major fault. After check up, the factory revised the color immediately. If we performed a quality check after the products are almost finished, this could be a major issue and the shipment will be delayed due to the revision of the issues found at the quality control.
So it is strongly recommended to do a quality check in the early stage of the production process. This quality control is required in China especially to avoid misunderstanding and faults in the further production process.