I have an external drive I use from time to time with various types of files.  I thought it would be interesting to see how Windows indexing would handle files and information on the external drive, so I checked its checkbox in the indexing options and let it index the drive.  Sometime later, I noticed my system disk space was dropping precipitously.  I looked at the disk space use and found the windows.edb database file had grown to more than 100GB.  After I unchecked the external drive in the indexing option and had Windows rebuild the index from scratch, my disk space was back to normal.