From Fixamac Software:
Spotless is a simple utility designed to enable and disable Spotlight content indexing of volumes with the click of a button.
Spotlight content indexing can cause major slow-downs on volumes that are used for backup purposes, video rendering, Photoshop scratch disks, and a wide variety of tasks that involve the transfer of large amounts of data. Spotless can effectively and indefinitely disable the indexing of volumes that you specify. Even if the volume is a removable device, the indexing status is remembered when you remount it - even on a different computer!
Simply adding volumes to Spotlight's privacy list does not achieve the same results as using Spotless. You may cause the Metadata Server to crash, and the volumes may be indexed the next time you mount them. Also, while adding volumes to the privacy list disables content indexing, it also prevents you from finding the files by name.
Spotless allows you to delete existing Spotlight indexes. This will free up the space used by the index files on volumes that are no longer being indexed. You may also delete indexes on volumes that are being indexed. This will cause Spotlight to reindex the volume - especially useful if your index becomes damaged.
If you are having difficulties with Spotlight indexing, it could be because the ".Spotlight-V100" directory on the volume has become damaged in some way. Spotless provides a quick way to delete this directory and set the initial indexing status of the volume. In order to set the indexing status, the ".Spotlight-V100" directory will be recreated.
Spotless will automatically find and delete the "mds-crash-state" file from selected volumes. The file may be created if the Metadata Server crashed or was unexpectedly closed during the indexing process. The presence of this file can prevent Spotlight from indexing the volume in the future.
Spotless allows you to see exact size the index directory on each volume.
Spotless also includes an on/off switch for Spotlight.