With the Workflow Extender Add On, you have the ability to capture user names in a table field and have those users added as participants to the form. 

Examples of where this Add On could be used, include processes that capture attendance such as Safety Meetings, Tailgate/Toolbox Meetings or Field Level Hazard Assessments or this could also be used in processes where you want to capture who has been assigned tasks and allow the individuals access to the form to review. 

In order for this to be configured, the nested referenced field must be linked to the Users List.

When the form is submitted to RPM, the users listed in the table field are added to the form as participants.