As Quoted by Google:

Web crawl – See errors and problems encountered by Google’s crawlers while accessing pages on your site.

Content analysis – See potential problems with site metadata, such as title and meta description information.

Mobile crawl – See errors and problems encountered by Google’s crawlers while accessing pages on your site created specifically for viewing on mobile cell phones.

Pretty cool hey? This allows you to test the Indexibility of your website in terms of fundemental architecture on page optimisation.