In the classical repertoire a majority of pieces modulate to the key of the dominant, and the introduction of an extra sharp (for example introducing the pitch F# to modulate from C to G major) can give the music lift and direction.
What does modulate to the dominant mean?
Modulation means to change key in the middle of a piece of music. In Leaving cert' we always modulate to the dominant in our melody writing. The dominant is the 5th note of the scale, or soh. ... This note is always Te in the new key and it will always have an accidental in front of it.