The concept of parallel keys is mainly used to simplify key signature notation, without significant impact on compositional expressiveness.

Parallel keys contribute by ensuring that all chord progressions remain diatonic to the original key, reducing chromatic alterations.

Parallel keys primarily function to maintain a consistent tonal center throughout a composition, limiting modulation possibilities.

Parallel keys allow for seamless modulation between major and minor tonalities with the same tonic, enhancing emotional contrast and harmonic richness.