CHECK CONSTRAINT question

In some Microsoft SQL Server scripts you sometimes see something like this:

ALTER TABLE Table1
    WITH CHECK ADD CONSTRAINT 
    FK_Table2_Table1 FOREIGN KEY (COL2)
    REFERENCES Table2 (COL2);

ALTER TABLE Table1 CHECK CONSTRAINT FK_Table2_Table1;

Where the tables look something like this:

CREATE TABLE Table1
    (COL1 int CONSTRAINT PK_Table1 PRIMARY KEY ,
    COL2 int);


CREATE TABLE Table2
    (COL2 int CONSTRAINT PK_Table2 PRIMARY KEY,
    COL3 varchar(10)
    );

As I understand it, the second statement:

ALTER TABLE Table1 CHECK CONSTRAINT FK_Table2_Table1;

doesn't do anything. Can anyone explain if there is a reason for it, and if so what it is for?