We all know that good links in to your site are a fantastic thing to have. But what about links out? It can be very difficult to convince colleagues that linking out (and potentially taking people away) from your site is desirable. However, linking out may have an SEO benefit, and is an easy thing to do, completely within your control. It’s not hard to find studies which seem to back up theories like “outgoing relevant links to authoritative sites are considered in the algorithms and do have a positive impact on rankings.”
So, when and where should you link out? To me, the obvious time to do it is when visitors are at a research stage, i.e. on your pages which are giving background information about a topic. If you’re setting up a page designed to show what an authority you are, why wouldn’t you provide evidence that you’re aware of supporting work?
The time not to link out is when visitors are in the sales funnel and shouldn’t be distracted. It’d be crazy to have a link just before your “contact us today” call-to-action saying “Why don’t you now go and read a Wikipedia page?”
And what should you link to? Obviously nothing competitive, although you could judiciously link to commercial sites in complementary fields. The ideal links would be to well-regarded, non-commercial research which backs up what you’re saying. There appears to be no truth in the rumour that links to and from government and educational sites are worth more than commercial ones, but it’s quite possible that the most helpful and safest links out will be in that direction.