Should I use an inline varchar(max) column or store it in a separate table?

I want to create a table in MS SQL Server 2005 to record details of certain system operations. As you can see from the table design below, every column apart from Details is is non nullable.

CREATE TABLE [Log]
(
[LogID] [int] IDENTITY(1,1) NOT NULL,
[ActionID] [int] NOT NULL,
[SystemID] [int] NOT NULL,
[UserID] [int] NOT NULL,
[LoggedOn] [datetime] NOT NULL,
[Details] [varchar](max) NULL
)

Because the Details column won't always have data in it. Is it more efficient to store this column in a separate table and provide a link to it instead?

CREATE TABLE [Log]
(
[LogID] [int] IDENTITY(1,1) NOT NULL,
[ActionID] [int] NOT NULL,
[SystemID] [int] NOT NULL,
[UserID] [int] NOT NULL,
[LoggedOn] [datetime] NOT NULL,
[DetailID] [int] NULL
)       

CREATE TABLE [Detail]
(
[DetailID] [int] IDENTITY(1,1) NOT NULL,
[Details] [varchar](max) NOT NULL
)

For a smaller data type I wouldn't really consider it, but for a varchar(max) does doing this help keep the table size smaller? Or I am just trying to out smart the database and achieving nothing?