Why I need the SqlCommandBuilder to update a table in Database?

Question

I watched a video tutorial and reprogrammed the same code. I have noticed that a didn´t understand, why I have to use the SqlCommandBuilder for updating a table.

    SqlDataAdapter sda;
    SqlCommandBuilder scb;
    DataTable dt;

    private void button2_Click(object sender, EventArgs e)
    {
        scb = new SqlCommandBuilder(sda);

        sda.Update(dt);
    }

I never use the variable scb. But when I comment out the scb = new SqlCommandBuilder(sda), then I get an error message:

"System.InvalidOperationException: A valid update command is required for an update."

Can someone explain, what function the CommandBuilder has?

In the remarks of the documentation it says:

The SqlCommandBuilder registers itself as a listener for RowUpdating events that are generated by the SqlDataAdapter specified in this property.

But I don´t understand when the CommandBuilder steps into action?