By promoting an element to be ‘planned’ you are making it available for other modelers to use, or even to create branches from it.
It should be done when a project reaches a significant milestone, so that it is sensible for other projects to plan their own solutions based on the planned change being delivered. Exactly when this happens in your projects will depend on your project delivery process.
You can setup a package in your model where ‘planned’ elements can be put (see Settings).
Note that once elements have been promoted to planned and other projects are able to branch from them, no further changes to those planned elements should be allowed. To prevent accidental changes, your model administrator may choose to move planned elements into a locked staging area, prior to implementation. Then if any further changes to those elements are needed before implementation, they can be managed by your project taking a new branch from the planned element and following the Portfolio Manager lifecycle as before. In this way the impacts and dependencies of your changes will be clearly visible to all model users.
This stage of the element lifecycle (promotion to planned) is optional. Elements can be moved directly from branched to implemented. An impact analysis is performed when the implement is performed, so you can always identify and communicate with any affected projects/modelers.