- To create a sense of drama or excitement: A song that suddenly changes key can create a sense of drama or excitement, or can help to build tension. For example, the song "Bohemian Rhapsody" by Queen changes key several times throughout the song, which helps to create a sense of drama and excitement.
- To accommodate the singer's vocal range: Some songs may be written in a key that is too high or too low for the singer's vocal range. In these cases, the song may be transposed to a different key that is more comfortable for the singer. For example, the song "I Will Always Love You" by Whitney Houston was originally written in the key of F major, but was transposed down to the key of E major for Houston's recording.
- To create a different mood or atmosphere: A song that is played in a different key can also create a different mood or atmosphere. For example, a song that is played in a higher key may sound more bright and cheerful, while a song that is played in a lower key may sound more dark and somber. For example, the Beatles song "Yesterday" is played in a lower key than many other Beatles songs, which helps to create a more somber mood.
- To add interest and variation: A song that changes key can also simply add interest and variation to the song. This can help to keep the listener engaged and prevent the song from becoming boring. For example, the song "Stairway to Heaven" by Led Zeppelin changes key several times throughout the song, which helps to keep the listener engaged.