What aspect does "allegro" primarily affect in a piece of music?

"Allegro" primarily affects the overall tempo of the performance, indicating a brisk and lively pace. In musical terminology, "allegro" is an Italian word that translates to "fast" or "cheerful," which signifies the speed at which the music is to be played. When a piece is marked allegro, it establishes a specific range of beats per minute, providing performers with guidance on how quickly to execute the music.

This tempo marking does not directly influence emotional impact, harmonic structure, or dynamics; instead, it sets the foundational speed and energy of the piece. While the tempo can certainly influence the emotional expression of the music, the term "allegro" itself specifically refers to the tempo aspect, distinguishing it from other musical elements.