Efficient Indexing in MongoDB 2.6` introduces a new query planner that enables index intersection, allowing users to reduce the number of indexes needed while maintaining rich features and low latency. This feature is particularly useful for ad-hoc queries where the shape of the queries cannot be predicted ahead of time. By processing individual indexes and intersecting the results, MongoDB 2.6 reduces memory usage and improves performance. While compound indexing will always be more performant if known in advance, index intersection provides a viable alternative in cases where the working set is large or memory is limited. With this feature, users can optimize their queries for better performance and reduce the overhead of indexes.