Two competencies overlap when they share a common learning objective (the same learning objective is attached to both of them). This enables you to reuse learning objectives that are prerequisites to more than one competency.
If two competencies have different Status settings but share a learning objective, this has repercussions for what can and cannot be done to the learning objective and the structure beneath it.
If a learning objective is attached to multiple competencies and any parent competency is Approved or Archived, then you cannot edit its properties or add or remove other learning objectives beneath it.