If you want your histories to remain accurate and complete, you should never actually delete any songs from your database.  When the time comes to stop playing a song, move it to a Rest or Icebox category instead.  MusicMaster only keeps a pointer to the song record in the history table.  If you delete the song record, all the histories for that song are removed from the history table, making them unavailable for use in the history browser, schedule editor, and on printed logs.  The same principle applies to non-music categories as well.  Keep your old promos and imaging stuff on ice.  Eventually you may want to delete songs that haven't been played in a very long time from your Rest category just to free up some space in your database.  That's fine, as long as you know they haven't been scheduled for a while -- at least long enough to keep them out of any history browser reports you might wish to run.