This article explains the difference between the options to delete Object data and Report Data in database management.
When selecting Delete Object Data then Exchange Server or Organization objects will be deleted from the MessageStats database. For example, this can be required when a new version of Exchange has been deployed to the environment and the old server information needs to be removed from the console and reports. In this example the records for this object do not need to remain in the database so the "Delete Object data" task can be used. If "Delete Object Data" is selected then all data regarding the specific object will be deleted including all historical data.
If "Delete Report Data" is selected then this will delete data only for a specific time period that can be specified. This option allows the deletion of historical data for specific time.
Please ensure before executing either of these procedures that a full backup is performed on the MessageStats database and that the database is not being written to during the delete process to avoid corruption of the information.