A planning folder is a virtual container that helps you organize and plan the work that goes into delivering a product.
You can create a hierarchy of planning folders to organize artifacts by product, release, iteration, etc. You can store artifacts from multiple trackers in a planning folder. This allows you to plan various stages of your project (i.e. releases, iterations, etc.).
Selecting an individual planning folder provides a view of all artifacts from all trackers within the selected planning folder.
The Planned For field identifies which product, release, or iteration the artifact is planned for, based on the planning folder that it is assigned to.
For example, in an Agile development environment, a project manager breaks down the prospective product into its component parts and looks at what it would take to deliver each one. When all the parts planned for a given iteration are finished, the product is considered complete for that iteration.
Some parts of a product can be developed more or less in isolation, but most depend on other parts. Tracking these relationships is one of the trickiest aspects of product development.
For example, you can only provide a graphical user interface for a shopping cart application if you also come up with a database for the customer's payment data to be stored and accessed. That in turn requires a data storage and backup solution of some kind. And so on.
Use a planning folder to track the dependencies among the parts of your project as each moves toward completion. As you work through the question of what depends on what, you'll move artifacts representing user stories into the appropriate iteration in the appropriate release. As you proceed, you'll find a pattern like this emerging:
Your planning folder lets you see at a glance the pieces of the work that support other pieces, and the pieces that depend on other pieces. Think of this as a "planning tree." If you are responsible for a development project, you can use this tree view to understand and predict the time and effort required to deliver a given set of features.