How does JCT clause 2.38 work?

Clause 2.38 of SBC/Q 2016 is the defects mechanism after practical completion: defects, shrinkages or other faults that appear within the Rectification Period and are due to materials, goods or workmanship not in accordance with the contract are listed in a schedule of defects, the Contractor makes them good, and clause 2.39 closes the process with the Certificate of Making Good. The Rectification Period starts on the date of practical completion stated in the Practical Completion Certificate under clause 2.30 and runs for the period stated in the Contract Particulars. During it the Architect/Contract Administrator may instruct the making good of individual defects, and at its end delivers the schedule of defects to the Contractor within the time the clause gives; after that no further instructions to make good can be given. The Contractor makes the scheduled defects good within a reasonable time and at no cost to the Employer. If the Architect/Contract Administrator, with the Employer's consent, instructs that some defects are not to be made good, an appropriate deduction is instead made from the Contract Sum. When the defects the Contractor was required to make good have been, the Architect/Contract Administrator issues the Certificate of Making Good under clause 2.39. The second half of the retention is released in the Interim Certificate that follows it, and the Final Certificate cannot be issued until it, the end of the Rectification Period and the statement of adjustments have all happened, so a late or withheld certificate holds up both the retention and the final account. What goes wrong is a schedule that includes items that are damage or wear rather than defects, an open-ended snagging list that keeps growing after the period has ended, retention withheld against defects that were never put on the schedule, and a Contractor who does not press for the Certificate of Making Good and so never starts the clock on its final payment.