Compare this with what happens when you simply delete a large volume of old data from a table and starting inserting new data.
Breaking the but the space that’s become available in the table will be in and around exactly that range of blocks – so the new index entries will probably end up looking very similar to the deleted index entries and inserted in and around the existing index entries for value ‘XXX’, so over time the index is unlikely to allocate much new space.
The scripts found in Esri Knowledge Base Article 24518 provide the SQL to both update statistics and rebuild indexes.
NOTE: Analyze Datasets: Updates the database statistics of base tables, delta tables, and archive tables, along with the statistics on those tables’ indexes.
This means that future inserts will soon start to reuse those table blocks.
Think about what this means for index entries – especially for non-unique keys.