The setting isn’t currently being used, but is planned on being used in the future.
Simply put, credit based systems allow your members to accumulate credits and spend them on services instead of using cash directly. As their credits increase either through buying or earning credits, they can then use those credits to buy additional access. Typically credits are earned either through one-time purchases, through subscriptions, or through performing activities. Credits are then redeemed either for an increased level of membership, or to buy access to content either on a permanent or temporary basis.