Folks, explain me, please the correlation of the content on a certain page and the whole site. Google ranks a page but not a web-site overall. That means if I add good unique content, Google will rank that newly created page high but other pages of the site will stay at the same level. At this point I can't trace the logic of adding new content at all. If I add it on a separate site page, how does it help to promote my web-site in general in Google's eyes?
If you don't know, them me explaining it is a waste of my time. Read threads in the forum and you will find more than enough reasons to add content.
Additional content allows you to target additional keywords. You can also interlink your pages so that the pages which target the longer tail keywords can link up to the pages that are targetting more competitive terms. So for example your new page on blue widgets can link up to your widgets page with the term "widgets" as the anchor text. Fresh content enables you to do so many things, like targetting more keywords, attracting more inbound links, spreading link juice around your site and keeping visitors on your site.
google focuses on page or pages, not the whose site, for example, if one page has unique content, the page maybe has good rank; if another page copie the other site page, the page maybe has bad rank, and the first page still has good rank.