Delete duplicates find songs that appear to be the same song and marks for deletions all the duplicates, no songs are actually deleted until changes are saved. By default Jaikoz identifies duplicates by looking for files with duplicate MusicBrainz Recording Ids and MusicBrainz Release Id, but in the preferences you can change this to find duplicates based on various combinations of Recording Id, Release Id and AcoustId. Jaikoz compares the duplicate files by their Audio Format, Bitrate, File size and Track Duration and deletes the files with the lowest quality. More information at Deleting Duplicates