It's necessary to mention, that customer birth date segmentation is applicable both with year and without it. For example, such flexible customer filtration will be useful in marketing work, namely in sms & e-mail distribution. So, you can single out a separate group for the customers, who have birthday, say, in 3 days, and set an SMS or e-mail sending with personalized offers. And such messages will be sent every year on birthday eve automatically. This way you get a loyal client, who, having got a discount in your eStore exactly, will come for shopping or for a family holiday gift.