Should I check if 'is not modified' for most responses?

I'm intrigued by this snippet:

public function indexAction()
{
    $response = $this->render('MyBundle:Main:index.html.twig');
    $response->setETag(md5($response->getContent()));
    $response->isNotModified($this->getRequest());

    return $response;
}

Should I do this whenever possible? I'm thinking that most pages in my websites could save bandwidth this way (though not CPU).