Web Developer Cum SEO Analyst Question:

Fetch is a Google tool which enables you to test how Google renders a URL on your site. You can 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.

This tool can be effectively used for the following purposes:

Troubleshooting webpages to improve the performance in SEO.
Submitting pages for indexing whenever the content is changed significantly.
Finding out the pages affected by any malware attack.