Self-referencing tables uses
Self referencing tables can be used to store hierarchical data.  For example, see my answer to this question.

You can also use self referencing tables to record non-hierarchical relationships which are one-to-one.  For example, let's say you have a PERSON table and you want to have a relationship is currently married to.  You might model this with an intersection table, or you might use a simpler self referencing relationship.