Why are tempo markings important in a musical score?

Tempo markings are crucial in a musical score because they indicate the speed at which a piece of music should be performed. These markings provide essential guidance to musicians on how fast or slow the music should be played, which directly influences the overall feel, mood, and interpretation of the piece.

For instance, a marking like "Allegro" suggests a lively and fast tempo, while "Largo" signifies a slow and broad pace. Accurately following these tempo indications ensures that musicians can achieve the composer’s intended emotional expression and dynamic contrasts. It sets the foundation for how rhythm and timing are interpreted, which are vital elements in music performance.

In contrast, the other options relate to different aspects of a musical score. The key signature defines the scale and notes used, instrument specifications detail which instruments should perform, and harmony changes indicate shifts in chords or musical structure. While all of these are important in their own right, they do not pertain to the essential function of establishing the speed of performance as tempo markings do.