Portfolio for JIRA allows you to add JIRA applications users as team members. You can also work with virtual users that are placeholders to play with what-if scenarios such as, adding a new hire to your team. In your plan you can create new teams and configure them by choosing their scheduling methodology and assigning them tasks. Teams can be plan-specific or shared across plans.
Private teams allow you to play around with what-if scenarios and plans that are not formally established.