A circular link or self-link links a page to itself directly or via one or more redirects. While a reactive attitude is to discourage, forbid and remove these, and a reflective attitude would avoid self-links wherever practical, the actual wiki best practice is to use them to deal with common reflexivity problems, especially those that arise when users fork wikis to pursue other goals. This use simply extends the common and desirable practice of making links when proposing new ideas.
When making self-claims about the best next step, self-links can be very useful. A direct link from a page back to itself, for instance, is a simple way to mark out a claim that applies to the page, as opposed to the topic name of the page, e.g. discussing which concerns are out of scope for that page. This is better than using italics for instance to indicate such meta concerns, or relying on categories or tagging, which will be just as hard to maintain and not as reliable as mention of the name of the page itself.
Self-links may also describe the topic. The simplest case is when a page describes an idea or option that isn't pursued, especially on talk pages where it's common to link to the name one is proposing. As long as the idea or option isn't being pursued, it's effective simply to redirect to anchor pages. Since wiki software can detect such links easily, it becomes easy to determine unpursued ideas.
As the idea develops into a legitimate option, via research and dialogue, it will acquire a name, illustrate one or more issues, and one or more detailed positions will be taken on which policy is ideal, which belong directly in project namespace if the project is very small, in a policy namespace if it's more formal, and in a position namespace if an organization protocol relying on IPA is in effect for this kind of decision. An open configuration project would definitely require argumentation frameworks of some kind if only to simplify issues into a parametrized contract.
Sometimes the position page may only be a redirect back to the original page where the position is taken, i.e. the page exists only to reflect the position in a normative namespace indicating a current debate.
Finally, to fork wikis implies that another goal is being pursued and therefore at least some ideas, options, positions/policies and configurations will be pursued that were previously not. Ideally no categories should change, no rewrites of page text, should have to happen, simply to expand the wiki in that direction rather than the other direction. An option or position that is not being pursued then can become a redirect rather than having to delete it, which better satisfies the need to avoid delete tactically.