Subscription Settings service provides multi-tenant functionality for service applications. It helps tracking subscription IDs and settings for services that are deployed in partitioned mode. It can be deployed through Windows Power Shell only. At the core of multi-tenancy is Site Subscriptions. A site subscription is a logical group of site collections that can share settings, features, and service data. Site collections for each tenant are grouped together with a Subscription ID. The subscription ID is used to map features, services, and sites to tenants and also to partition service data according to tenant. The Subscription Settings service application is responsible for keeping track of multi-tenant services and subscription IDs.