This is a mechanism that helps to minimize the purchase process. If a customer has already purchased in an online store (or has created an account and provided their card data), a merchant may allow them to make next purchases without filling in the information again.
The main idea behind this solution is to simplify the purchase process and improve its experience, which results in greater income for the merchant.
You can read more about card data storage on [PayLane Developer Zone][devzone-com-cards-card-data-storage].
Card Data Storage are free at PayLane; merchants are only charged the regular transaction fees.