Java では、Thread.start() の代わりに Thread.run() を呼び出すのはどのような場合ですか?

public class CallRunMethodTest extends Thread {
   @Override
   public void run() {
      System.out.println("In the run() method: " + Thread.currentThread().getName());
      for(int i = 0; i < 5 ; i++) {
         System.out.println("i: " + i);
         try {
            Thread.sleep(300);
         } catch (InterruptedException ie) {
            ie.printStackTrace();
         }
      }
  }
   public static void main(String[] args) {
      CallRunMethodTest t1 = new CallRunMethodTest();
      CallRunMethodTest t2 = new CallRunMethodTest();
      t1.run(); <strong>// calling run() method directly instead of start() method</strong>
      t2.run(); <strong>// calling run() method directly instead of start() method</strong>
   }
}

In the run() method: main
i: 0
i: 1
i: 2
i: 3
i: 4
In the run() method: main
i: 0
i: 1
i: 2
i: 3
i: 4