From discussing beloved pieces of music (and also my own compositions) with other people, I have gathered that I hear music differently from most people. A major point of divergence is how we experience dissonance. Most of my life I have been at least a little mystified by the point of view that holds that dissonance is ugly or harsh. I hear dissonance, and its relationship to its opposite (consonance), quite differently. And though music, for me, has always and only been something that I can hear - I can never fully understand the way synesthetes experience music with senses other than hearing - what I hear when I experience dissonance can best be described by appealing to the other senses.
Consonance is like a point of stasis or equilibrium, a point of departure or arrival. Different types and degrees of dissonance point the way along the journey between points of consonance. Dissonance makes manifest the forces that push and pull music toward its goal. To be sure, too much dissonance may give a piece of music a sense of aimless drifting or rushing about with no end or point of rest. But not enough dissonance means the music never seems to go anywhere.
If music is a fluid, consonance thins it and allows it to run clearly, smoothly and freely. Dissonance, on the other hand, thickens it and makes it viscous and stretchy. Maybe too much dissonance gums it up, but if there is not enough dissonance, the music runs away and leaves nothing behind.
It is an interesting fact that a dissonant note can make a chord sound louder, even when there is no change in loudness; can make an instrument or voice stand out of an ensemble texture, even though it isn't playing or singing any louder or brighter than the others. Dissonance creates friction.
Dissonance is like a splash of bright light that dazzles your eyes; where you seek relief in a cool shade, that is consonance. I have often heard dissonance, such as a chord that has an added note, as a kind of brightness or an accent.
Dissonance is like a dash of salt that gives flavor to a bland dish; consonance is rather like sugar. The two can work together to take the edge off each other, but if one overpowers the other, the flavor is ruined. I recently wrote an organ piece with a hymn tune in the pedal part. About 2/3 of the way through writing the piece I realized that the right-hand part, accompanying the hymn tune, gave the piece a syrupy sweet sound that rang false. So I went back and wrote in a left-hand part for the express purpose of taking the edge off the music's sweetness. I thought of this new melody as a dash of salt.