I learned this the hard way, a few weeks ago i had about 1400 indexed pages, it was always a bit odd because i knew i was blogging alot but not that much, so i started going through my serps for blueverse and i saw a ton of search queries, tags and categories within the serps with no unique description in the results, this is a really really bad thing to have in your serps if you are targeting for some tough keyword, since i was using All in one seo pack for wordpress i easily no followed all search queries, tags and categories.
This gave me a really good boost within the serps which is resulting in me ranking as follows:
Decreasing the number of non-unique pages from your serps gives more authority to your currently authoritative pages and boosts their rankings, although a few rankings up there still have to come up from the slump, the others are doing better then before.
