What happens when too many pages are added to Google
A recent video that went semi-viral in the SEO world is a video by Google.
Matt Cutts revealed in one of this answer to question videos that adding too many pages to a website in a short time could cause a manual review and subsequently result in a manual penalty. A manual penalty is when someone from Google comes to your website and reviews the site manually. They usually go through a list of questions and at the end, if your site is not up to scratch you might be given a stiff Google manual penalty. Often people build a website and while they are building the website they put the site in maintenance mode.
While the site then is in maintenance mode they continue to add more pages and sometimes people add 100's of pages at once. When the site finally is released into the wild, search engines only see thousands or hundreds of new pages going live at once as they scan through the website for new content. When Google sees a page go live the search engine indexes it. Simple as that.
Google can, however, handle thousands of links and pages going live at once, it's not like their search engines will crash or anything. What happens is, when your site has thousands or maybe even hundreds of pages going live all at once it sets off an alert over at Google. The reason for this is most probably that Google believes that thousands of pages can't be quality if they are made at such a fast pace. Thousands of pages can't be added at such a rate that are good quality, highly informative and good content by a normal group of or even single individuals.