There could be many pages on your site that you would not want Google to crawl and hence not include in the search results. While applying noindex or removing it via robots.txt file is a solution, some old pages might still continue to appear in the results and hence it is suggested to remove them via the URL Removal Tool that’s there in the Google Webmaster Tools Dashboard.
The URL Removal tool also comes in handy when you need to urgently remove a page from Google that has mistakenly gone public. So far, doing this wasn’t straight-forward. Google wanted you to first block the URL or remove the page, and then submit your request. Not anymore.
From now on, you can just submit a URL in the Remove URL section in Webmaster Tools -> Site Configuration -> Crawler Access, and Google will remove it from its index. However, Google might continue to crawl it for the next 90 days, and in case you want to re-include the page in the index, you may quickly revoke your removal request from your webmaster dashboard.
This temporary block ensures that you don’t need to go through the process of removing or non-indexing a page, and also lets you quickly re-include the page if you made a mistake by removing it.
However, if you want to permanently remove the page, the requirements remain the same. You need to block it from your end too apart from submitting the removal request with Google. It could be a robots.txt block, having it return a 404 error or applying a noindex meta tag. Any of these should work. But you need to do it after submitting the removal request.
Keep in mind that URL removal from Google is something you should not be doing in haste. Be careful and only remove a page from Google’s index when you really want to.