A thread at Google Webmaster Help forums has a webmaster concerned that Google isn’t allowing him to manually use the submit to index in the fetch in render tool in Google Webmaster Tools for all the URLs on his site. As you know, there is a limit to how often you can use that feature per day/per month.

In response to the webmasters concern, Google’s John Mueller said on the thread:

Yep, that is what GoogleBot does, it is all about seeking out and consuming new and changed content and web pages. So if you really want to expedite it for a large number of pages, use Sitemaps.

Forum discussion at Google Webmaster Help.