What is the purpose, creative intention, and performance style of The Sound of Music and West Side Story?

Both The Sound of Music and West Side Story are performed as musicals, meaning singing and dancing are an essential part of their storytelling technique. Personally, this is one of my favorite film styles.
These movies are distinctive in that they use the platform of a musical style to tell a serious story. The Sound of Music, set in 1938, tells of the von Trapp family having to flee Austria because of conscientious objection to joining the German Navy during the Nazi regime. West Side Story, a Romeo and Juliet-inspired tale set in the 1950s, explores such social problems as prejudice and animosity between those of different ethnic backgrounds and the repercussions of gang violence.
The creative intent of such musicals is to both further the plot and develop the characters by means of song and dance. For example, in The Sound of Music, the song "Maria" is used to give us insight into the protagonist's character—such as her liveliness and youthful energy. In West Side Story, the song "America" gives context to the story by examining the pros and cons of being an immigrant in that country.