why get_header() is calling do_action() for get_header…?

Hi all,

i am confused for do_action( ‘get_header’, $name ); in

function get_header( $name = null )
{
	do_action( 'get_header', $name );

	$templates = array();
	$name = (string) $name;
	if ( '' !== $name )
		$templates[] = "header-{$name}.php";

	$templates[] = 'header.php';

	// Backward compat code will be removed in a future release
	if ('' == locate_template($templates, true))
		load_template( ABSPATH . WPINC . '/theme-compat/header.php');
}

what is need to call do_action inside get_header()…..?