Answer:
These key signatures provide a convenient alternative to writing out all of the necessary accidentals for a given key. Instead of writing a b before every B, E, A, D, and G (as necessitated by the Db-major scale), the key signature instructs the performer that every B, E, A, D, and G on the staff are to be lowered a semitone unless otherwise noted. Compare Example 8–1 with the following, which writes out the required accidentals instead of using a key signature. Notice how much more cluttered the score appears:
