Answered: Should I allow google to Crawl everything ?

Sure, if your site is open to the public I don't see why not.

If you have any content you're not certain if it should or should not be indexed, you can block search indexing with 'noindex' 

Let's say you don't feel like sharing profile pages because it has too sensitive information about your users. To prevent all bots from indexing your User pages, you would open your  qa-theme.php  file and add the following code.

public function head_metas()
{
    if ($this->template === 'user') {
        $this->output('<meta name="robots" content="noindex">');
    }
    parent::head_metas();
}

This if you don't have a  head_metas()  function in your  qa-theme  already of course. If you have, you'd just paste that output in. If you only want to block Google from indexing, then you'd do:

<meta name="googlebot" content="noindex">

Read more about indexing here: https://support.google.com/webmasters/answer/93710?hl=en