Reward cards let you issue (and manage) points on LINE as an incentive for users to purchase goods, use services, or visit your store.
Using LINE solves the usual problems that come with physical point cards; users won't refuse them because they take up space, and you don't have to spend money printing them. Also, because they're digital, you have access to features for viewing and managing statistical data, making it easier to efficiently earn repeat customers.
Issuing reward cards can be a useful tool for attracting new customers too, since you can send them to users who haven't even visited your store yet.