In almost every post that you publish, there is no reason why you can’t find a place to fit in a link to a previous post, once your archive gets above a good twenty or thirty posts.
Why would you want to link to previous posts? Well, not only is there a search engine benefit, but it can be quite useful to your visitors interested in other similar articles, or other opinions on your site.
If you are using plugins to link to other posts in a related posts area on a page, it can be useful but not as optimized as doing it manually. When doing it yourself, you have control over the keywords you use, the placement of the link and how many links you use would be custom to each post.
Not to mention, how much more relevant your own custom chosen links will be over those selected by a WordPress plugin, but that is just my two cents on the matter.
Link to yourself often for no other reason but to be a great service for new readers who weren’t around when you posted previous content.
And yes, this is something I still need to work on…
(this post doesn’t have any links because I didn’t have any previous content that I felt compelled to link to.)