Sync Gateway is an integral component of the Couchbase Mobile stack, serving as a mechanism for organizing and securing document access through channels. Channels allow for efficient categorization and control of document flow, enabling users to assign documents to multiple channels for structured data management. The default sync function in Sync Gateway automatically creates channels based on document properties, but clients can request specific channels during replication, with access being determined by user authentication or assigned roles. The relationship between clients and Sync Gateway is not symmetrical, which can result in clients being able to write documents they cannot read. Additionally, Sync Gateway handles scenarios where access to documents is lost by creating a tombstone revision, which signifies removal rather than deletion, ensuring that clients like Couchbase Lite behave as if the document no longer exists. Understanding these nuances is crucial for effectively utilizing Sync Gateway to address complex data synchronization and offline use challenges within Couchbase Mobile.