XnView Software

I often optimize my catalog file to get the best performance.
Today I tested purge all thumbnails (=clean all thumbnails from database) and purge file data (=clean meta data from files?).
I do not see any difference between both functions. Both clean up my database from thumbnails and file informations.

'Purge all thumbnails' remove thumbnails from database
'Purge file data' remove file informations from database, in this case thumbnail will be invalid too