This is an improvement to make a certain use case more efficient. When there is a parent node with frequently added and removed child nodes, the reading of the current list of child nodes becomes inefficient because the decision whether a node exists at a certain revision is done in the DocumentNodeStore and no filtering is done on the MongoDB side.
So far we figured this would be solved automatically by the MVCC garbage collection, when documents for deleted nodes are removed. However for locations in the repository where nodes are added and deleted again frequently (think of a temp folder), the issue pops up before the GC had a chance to clean up.
The Document should have an additional field, which is set when the node is deleted in the most recent revision. Based on this field the DocumentNodeStore can limit the query to MongoDB to documents that are not deleted.