MongoDB currently supports TTL indexes for removing old documents from a collection. There are some use cases where it would be useful to extend the concept of TTL behaviour to the collection as a whole.

A couple of examples:

• Automatically dropping old collections when storing time series data using the schema advocated by our High Volume Data Feed reference architecture.
• Automatically cleaning up temporary aggregation results created by aggregation pipelines with the $out operator. If each aggregation query outputs to a different temporary collection, the cached aggregation result is most efficiently cleaned up by simply dropping the collection.