If the purge was accompanied by a clustered index rebuild OR if the choice of keys in the clustered index is right, the table should resize after the purge. And yes, given the B tree structure of indexes, the amount of I/O incurred while resolving queries can drop drastically. If you have the index stats before and after, that should show it too. Last but not the least, how do you know that the query load on your DW is a constant ? What if the amount of queries againsst this table has dropped recently ? You may want to ascertain that as well, before drawing any conclusions.