Free verse sounds more conversational, like people talking. Free verse creates a more American style. Free verse is less formal. Free verse conveys whitman's ideas about individualism, life, death, or the american landscape.
There are many critics sharing their ideas and opinions about Whitman's decision in using free verse to support his themes. They think that this is to create a unique style of writing that blends journalism with music, oratory, and other cultural influences to transform American poetry.