Dúvida sobre manipulação de arquivo

Estou com uma dúvida nesse flush() alguém pode me explicar?

package br.com.aprendendo.javacore.Vio.test;

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;

public class BufferWriterTeste {

    public static void main(String[] args) {
        File file = new File("file.txt");

        try (FileWriter fileWriter = new FileWriter(file);
             BufferedWriter bufferedWriter = new BufferedWriter(fileWriter)) {
            bufferedWriter.write("O salndo no arquio...");
            bufferedWriter.newLine();

            bufferedWriter.flush();
        } catch (IOException e) {
            // TODO: handle exception
        }

    }
}