In Couchbase Server 6.6, Flex Indexes offer a flexible schema that allows developers to create indexes without having to define the structure of their data in advance. This enables queries with complex predicates involving multiple fields, reducing the need for manual index management and improving query performance. By using Flex Indexes, developers can avoid the overhead of maintaining multiple GSI indexes and take advantage of advanced features such as FTS (Full-Text Search) indexing, which provides better performance for queries that involve full-text search or complex predicates. The process of setting up a Flex Index involves specifying the index name, bucket, JSON type, and document type, and providing hints to guide the query engine in choosing the most suitable index. With Flex Indexing, developers can write more flexible and efficient queries, reducing the risk of performance issues due to incorrect indexing or missing indexes. By leveraging Flex Indexes, developers can improve their overall development experience with Couchbase Server 6.6.