It can be quite tempting to hoard all of your hard earned page rank in order to perform better in search results. After all, if Google sees page rank as a measure of importance you’re going to want as much as possible right? It certainly does help to have a lot of pagerank flowing through your site and I wouldn’t advocate linking out too much from your important pages. That said, If you have no outbound links from your site whatsoever then think about how that looks to the search engines.
The only way that they can then associate you with other sites is by looking at your inbound links.This is okay if you have links from authoratitive sites already but if not it can be worth linking out to useful sites that are in the neighborhood you want to be associated with. The added bonus to linking out is that it can differentiate your site from serps hungry spammers who will not be wanting to link out at all. It will make you look like you are a natural part of the community instead of someone who’s trying to barge their way in.
There is the commonly held theory that if you’re linking out to other sites that you will lose your users but if your site has regular content worth viewing your users will be back. Im not saying that if you are selling mobile phones that you should link out to another mobile phone shop but you can usually offer your users links that will help inform them about a purchase to strengthen your chance of selling. e.g. If you’re selling a memory foam mattress it may be worth linking out to a description of how memory foam works and how it can benefit your customers health. Your users will get some extra information and Google, Yahoo, Bing etc will see that there is a connection between the two sites.
I wouldn’t advocate linking out heavily across your site but there is more to be gained than losing page rank.