When you are linking workflows via workflow nodes, any variables set during the session will be available to any sub-workflow.
For example, if you ask for a name and email in a parent workflow, and then use a workflow node to go to a sub-workflow, the name and email variables are available to the sub-workflow, or any other workflows launched during the session.
Any variables set in the sub-workflow are also available to the original workflow if you return to the original workflow.