It’s great to have a site that naturally attracts good quality inbound links. This can because you’ve provided great content or something unique for visitors to engage with. The result of these back-links provides your site with an endorsement of trust and in some cases; PageRank. In a manner of speaking, the ‘google juice’ has spilled from these other sites to yours.
Your PageRank is also effected by your outbound links and spills away accordingly. Upon knowing this you may immediately have to consider how you can save your juice. If you think for a second that making all your outbound links ‘nofollow’ will save your juice – it comes at an expense in terms of what Google thinks of your website. Forward, a penalty or worse. Why? You are basically telling Google you don’t trust anyone you link to. Wikipedia follows this path, and employs primarily ‘nofollow’ links, and still ranks impressively well. But, wikipedia is seemingly that ‘great content’ we hear so much about.
Google advises to use nofollow on paid links. Basically Google expects any paid relationship to be visible to both search engines and real users alike. This is not the reality of the web as we know it.
Search engine robots aren’t capable of signing-up or registering so using ‘nofollow’ on links to external registration or sign-up pages is a good way to steer Google’s crawling in the direction of pages that matter for your search visibility.
The BBC (with a PR of 9) has recently embraced more outbound links to offer readers & users alternative views. But, outbound links from the BBC, at the time of writing this piece, are passing through two redirect scripts using a 302 redirect which is highly unlikely to pass any PageRank. This is an advanced example of saving Google juice.
For your website, and with an understanding of how spilling your juice affects your Search Engine Optimisation, consider fewer outbound links on pages such as the homepage, and key top level landing pages.