Experimenting with SQL NULL vs. blank

CreateDB.sql

USE [master]
GO
/****** Object:  Database [Experiments]    Script Date: 11/30/2014 4:39:05 PM ******/
CREATE DATABASE [Experiments]
GO
ALTER DATABASE [Experiments] SET COMPATIBILITY_LEVEL = 110
GO
ALTER DATABASE [Experiments] SET ANSI_NULL_DEFAULT OFF 
GO
ALTER DATABASE [Experiments] SET ANSI_NULLS OFF 
GO
ALTER DATABASE [Experiments] SET ANSI_PADDING OFF 
GO
ALTER DATABASE [Experiments] SET ANSI_WARNINGS OFF 
GO
ALTER DATABASE [Experiments] SET ARITHABORT OFF 
GO
ALTER DATABASE [Experiments] SET AUTO_CLOSE OFF 
GO
ALTER DATABASE [Experiments] SET AUTO_CREATE_STATISTICS ON 
GO
ALTER DATABASE [Experiments] SET AUTO_SHRINK OFF 
GO
ALTER DATABASE [Experiments] SET AUTO_UPDATE_STATISTICS ON 
GO
ALTER DATABASE [Experiments] SET CURSOR_CLOSE_ON_COMMIT OFF 
GO
ALTER DATABASE [Experiments] SET CURSOR_DEFAULT  GLOBAL 
GO
ALTER DATABASE [Experiments] SET CONCAT_NULL_YIELDS_NULL OFF 
GO
ALTER DATABASE [Experiments] SET NUMERIC_ROUNDABORT OFF 
GO
ALTER DATABASE [Experiments] SET QUOTED_IDENTIFIER OFF 
GO
ALTER DATABASE [Experiments] SET RECURSIVE_TRIGGERS OFF 
GO
ALTER DATABASE [Experiments] SET  DISABLE_BROKER 
GO
ALTER DATABASE [Experiments] SET AUTO_UPDATE_STATISTICS_ASYNC OFF 
GO
ALTER DATABASE [Experiments] SET DATE_CORRELATION_OPTIMIZATION OFF 
GO
ALTER DATABASE [Experiments] SET TRUSTWORTHY OFF 
GO
ALTER DATABASE [Experiments] SET ALLOW_SNAPSHOT_ISOLATION OFF 
GO
ALTER DATABASE [Experiments] SET PARAMETERIZATION SIMPLE 
GO
ALTER DATABASE [Experiments] SET READ_COMMITTED_SNAPSHOT OFF 
GO
ALTER DATABASE [Experiments] SET HONOR_BROKER_PRIORITY OFF 
GO
ALTER DATABASE [Experiments] SET RECOVERY SIMPLE 
GO
ALTER DATABASE [Experiments] SET  MULTI_USER 
GO
ALTER DATABASE [Experiments] SET PAGE_VERIFY CHECKSUM  
GO
ALTER DATABASE [Experiments] SET DB_CHAINING OFF 
GO
ALTER DATABASE [Experiments] SET FILESTREAM( NON_TRANSACTED_ACCESS = OFF ) 
GO
ALTER DATABASE [Experiments] SET TARGET_RECOVERY_TIME = 0 SECONDS 
GO
USE [Experiments]
GO
/****** Object:  Table [dbo].[Table1]    Script Date: 11/30/2014 4:39:05 PM ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Table1](
	[SomeField] [nchar](255) NULL,
	[SomeId] [int] IDENTITY(1,1) NOT NULL
) ON [PRIMARY]

GO
/****** Object:  Table [dbo].[Table2]    Script Date: 11/30/2014 4:39:05 PM ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Table2](
	[OtherField] [nchar](255) NULL,
	[OtherId] [int] IDENTITY(1,1) NOT NULL,
	[Ref] [int] NULL
) ON [PRIMARY]

GO
/****** Object:  Index [ClusteredIndex-20141130-163657]    Script Date: 11/30/2014 4:39:05 PM ******/
CREATE UNIQUE CLUSTERED INDEX [ClusteredIndex-20141130-163657] ON [dbo].[Table1]
(
	[SomeId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
GO
/****** Object:  Index [ClusteredIndex-20141130-163628]    Script Date: 11/30/2014 4:39:05 PM ******/
CREATE UNIQUE CLUSTERED INDEX [ClusteredIndex-20141130-163628] ON [dbo].[Table2]
(
	[OtherId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
GO
SET ANSI_PADDING ON

GO
/****** Object:  Index [NonClusteredIndex-20141130-163718]    Script Date: 11/30/2014 4:39:05 PM ******/
CREATE NONCLUSTERED INDEX [NonClusteredIndex-20141130-163718] ON [dbo].[Table2]
(
	[OtherField] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
GO
/****** Object:  Index [NonClusteredIndex-20141130-163800]    Script Date: 11/30/2014 4:39:05 PM ******/
CREATE NONCLUSTERED INDEX [NonClusteredIndex-20141130-163800] ON [dbo].[Table2]
(
	[Ref] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
GO
USE [master]
GO
ALTER DATABASE [Experiments] SET  READ_WRITE 
GO

GenerateData.sql

USE Experiments;

SET NOCOUNT ON;

DECLARE @count int;
DECLARE @str nchar(255);
SET @count = 0;

WHILE @count < 15000
BEGIN
	INSERT INTO dbo.Table1(SomeField)
	VALUES (NULL);
	INSERT INTO dbo.Table2(OtherField
		,Ref)
	VALUES (NULL
		,@@IDENTITY);
	SET @count = @count + 1;
END

SET @count = 0;
WHILE @count < 15000
BEGIN
	SET @str = CONVERT(nchar(255), NEWID());
	INSERT INTO dbo.Table1(SomeField)
	VALUES (@str);
	INSERT INTO dbo.Table2(OtherField
		,Ref)
	VALUES (@str
		,@@IDENTITY);
	SET @count = @count + 1;
END

SET @count = 0;
WHILE @count < 15000
BEGIN
	SET @str = '';
	INSERT INTO dbo.Table1(SomeField)
	VALUES (@str);
	INSERT INTO dbo.Table2(OtherField
		,Ref)
	VALUES (@str
		,@@IDENTITY);
	SET @count = @count + 1;
END

Queries.sql

USE Experiments;
SET statistics time on;

SELECT count(*)
FROM dbo.Table1 AS tbl1
LEFT OUTER JOIN dbo.Table2 AS tbl2
ON tbl1.SomeField = tbl2.OtherField
WHERE tbl2.OtherField <> '';

SELECT count(*)
FROM dbo.Table1 AS tbl1
LEFT OUTER JOIN dbo.Table2 AS tbl2
ON tbl1.SomeId = tbl2.Ref;
WHERE tbl2.OtherField <> '';

SELECT count(*)
FROM dbo.Table1 AS tbl1
LEFT OUTER JOIN dbo.Table2 AS tbl2
ON tbl1.SomeId = tbl2.Ref;

SET statistics time off;