For what purpose is an organisation permitted to use a customer’s date of birth?

It is used to know the exact age of customer for a better analysis and segmentation. It's also used as an incentive to provide valuable gift on birthday for customer satisfaction

To wish them happy birthday and giving handsome discounted coupons.

To i dentfify servce prefarances, as customers choice and use of products and services change with their changes in age;  so organisations  ought to have customers details of date of birth, so that  to serve them better, with thier advancement in age;forv long term customer retention;

It may be ustilized in the data base for understanding and evaluating the customer's need and then solution.