This question was asked numerous times and answered by SEO experts everywhere. Now, the answer comes directly from Google. In his last video, Matt Cutts, head of the Google Webspam Team, explains that a large number of pages can open up multiple opportunities, but it’s not sufficient for better organic results.
“I wouldn’t assume that just because you have a large number of indexed pages that you automatically get a high-ranking. That’s not the case.”, Cutts said.
He further on explains that a large number of pages could attract a larger number of back-links and therefore a higher Page Rank. This could, in fact, be a helpful factor in the ranking of the website. Of course, this part is tricky. Too many links could raise a red flag and your website could receive an unpleasant penalty.
“Now typically, if a site does have more pages, it might mean that it has more links pointing to it, which means it has higher page rank. If that’s the case, we might be willing to crawl a little bit deeper into the website.”
Obviously, the more pages your website has, the more space you have for your keywords, this proving to help rank on individual queries. Again, being overzealous could attract a penalty here as well. A large number of keywords is called “keyword stuffing” and it’s unnatural and punishable according to Google.
“It is the case that if you have more pages that have different keywords on them, then you have the opportunity where they might be able to rank for individual queries that the user has.”