Use of ANSI_NULLS in Sql Server

SET ANSI_NULLS ON
IF NULL = NULL
 BEGIN
   PRINT 'TRUE';   
 END
ELSE
  BEGIN
    PRINT 'FALSE';
  END

Output:- FALSE 

SET ANSI_NULLS OFF
IF NULL = NULL
   PRINT 'TRUE';
ELSE
   PRINT 'FALSE';

SET ANSI_NULLS OFF
IF NULL IS NULL
   PRINT 'TRUE';
ELSE
   PRINT 'FALSE';

Output:- TRUE 

SET ANSI_NULLS ON
IF NULL IS NULL
   PRINT 'TRUE';
ELSE
   PRINT 'FALSE';

Output:- TRUE