MongoDB is introducing time-to-live (TTL) collections, which allow for controlled document expiration, reducing the need for cron jobs and improving database performance. The feature will be available in MongoDB 2.2 and can be tested in the latest development release. TTL collections enable developers to set an expiration date for documents, after which they are automatically removed from the collection. This allows for efficient management of data that is no longer needed or relevant. The technology has applications in various scenarios, such as session management, caching, and data archiving, where timely removal of outdated information is crucial.