One of the questions in dispute between SEO experts is the question "Is outbound links from my site to other sites are beneficial or harmful to me?"
There are two main reasons against Knesset outbound links to other sites: (process server)
PR leakage - To understand the issue of "leakage PR", read the first article about the importance of the page (PageRank). In a nutshell we can say that every page on your site has the power to "vote of confidence". A link to the specific considered by Google a vote of confidence on the page you link to it. If you link to a page on another site, you supposedly "wasting" their voting power on a page of another site instead of the pages on your website.(process server)
Members leakage - link to other websites cause your users to leave your site for the benefit of another site. While the link can be made so that the new site will open in a new window, but users do not like it, and beyond that, they can go to the new and forget about your site.(process server)
The main reason for outbound links is somewhat philosophical. Proponents argue that it is impossible for the search engines do not encourage users to link to other sites. But there is no proof of the justice of this argument.
Link out to bad neighborhood
When deciding to link to another site, you must be careful because a link to pages that are punished. Website offenses committed by search engines dictated rules for what you can do and what is not optimized, may find themselves in a kind of "black list". It is often said that such sites have turned into "bad neighborhood".
Although references exported from "bad neighborhood" can not harm your site, but turning to "bad neighborhood" Absolutely can be harmful.
My rule of thumb: Do not turn the pages with PR0 but after checking the code of the page.
For more information about, you should read the article penalties on Google.
Rel = nofollow tag
Online there are many sites that allow users to add comments, notes, signatures guest books etc. Many publishers have used this option to enter these sites and put them messages that include a link to their sites to improve their position in search engine results. This phenomenon has caused pollution browsing experience of users innocent. This action is called spam messages.
To combat the problem, Google announced the addition of a new tag nofollow. The tag can be added to any link on the site, and through "announce" that link quality is questionable, and that there does not have to follow and / or refer to it when determining site location from which the link.
Many sites have begun to use this tag to make "sculpting PageRank" (foreign languages: PageRank Sculpting) and block links to internal pages that do not like to strengthen, but on 15 June 2009, Matt Cutts, head of Web-Spam Google has officially announced that this tag the -nofollow is used more like a sponge than a patch. In other words, using it for sculpture PR irrelevant.