The Google Fetch is a Google tool which enables you to test how Google renders an URL on your site. In case you want to use Google Fetch to see whether Googlebot can access a page on your site, how it renders the page, and whether any page resources are blocked to Googlebot
The best thing to do is to keep your pages crawlable. If you make a change to a specific page, run it through the fetch & render at least once to be sure that it’s available for Googlebot, unless you don’t want it to be. you can request index for your particular URL by it.