A tailor who has been open ten years knows which customer wants the sleeve a little loose, whose daughter is getting married next year, who pays on delivery and who has to be reminded twice. That is a customer relationship system, and it is a good one.
It has two problems. It does not scale past the number of people one person can hold, and it cannot be handed to anybody else. The day the shop is busy enough to need a second person at the counter, everything that made the service feel personal is stuck with whoever is not at the counter that day.
It is also silent about absence. You notice the customer standing in front of you; nobody notices the one who has not come since Deepavali. That customer has not complained and has not gone anywhere dramatic — she simply stopped, and she will not appear in any register, because a register only records what happened.
Writing it down is not about replacing the memory. It is about making the memory available at the counter when the owner is out, and making the silence visible. What that is worth is worked through in getting tailoring customers to come back.