What is the significance of inserting discordant notes in written music?

Part of
the reason for inserting notes of dissonance within any musical piece would be to enhance the
overall tonal quality of the work.  Discordant notes awaken the audible sensibilities of the
listener, and, in many ways, can begin a sense of questioning about the music.  How the notes
were inserted, why they were placed, and creates a level of potential "uneasiness" in
the work, allowing the listener to actually become more engaged in the listening process.  From
the composer point of view, these notes' inclusion represent something more than the purely
harmonious sounds in any piece.  On a more symbolic leve, these notes' inclusion
could...