Couchbase 4.5 offers three scan consistency options for N1QL queries, allowing users to make trade-offs between speed and completeness in data retrieval. The default option, NotBounded, prioritizes performance by not waiting for index updates before executing queries, which can result in incomplete data if recent changes haven't been indexed. RequestPlus, on the other hand, provides complete results by waiting for all document changes and index updates before running a query, sacrificing performance for accuracy. The new AtPlus option introduced in Couchbase 4.5 serves as a middle ground, offering better performance than RequestPlus by waiting only for specific documents to be indexed, known as "read your own write" (RYOW), thus providing a balance between speed and data accuracy. The blog post provides code examples for each option to demonstrate their effects and highlights the need for enhanced durability settings when using AtPlus.