The addition of the sub-document API to Couchbase 4.5 has enabled efficient data structure support in Couchbase, allowing developers to store complex data structures such as lists, queues, and dictionaries within a single document, reducing the need for loading and saving entire documents. The Couchbase .NET SDK provides implementations for these data structures, including List, Queue, and Dictionary, which can be used to efficiently manage data by only sending specific parts of the document over the wire, rather than the entire document. These data structures are designed to be more performant than traditional whole-document approaches, making them a valuable tool for developers managing large datasets in Couchbase.