The Preview Range window will let you select what range of records will be used in the softproof. Previewing a smaller range will make the preview faster but will display less pages. On the other hand, previewing a larger number of records will take more time but will let you check the validity of more records.
Changing the preview range will not affect the number of records that will actually be generated in the output, it will only change the number of records displayed in the softproof.
To change the range of records to preview: