There may be a case where a common process will need to be run on all existing items in a list. This can be achieved by a parent workflow triggering a child workflow to run on the next item in a list to and so on, causing a chain-type of effect. The main advantage of this is less server load as only one workflow runs at a time. This type of workflow is usually executed once, and updates each item as required.
In this tutorial, you will create a parent workflow that queries a list, and then determines whether or not a child workflow should be started based on a filter. For each item returned by the query, a child workflow is started which is tasked with updating a field within the item.
I suppose this could work. However I do not like those situations where I have to pass a username+password for a service to work. When someone changes that password, there is no reason they should need to go through all workflows to be sure they still work.
After all: It is one workflow starting another.
I think it is bad design.
In Central Admin you can create a workflow constant containing the login credentials. You can then assign these login credentials in the workflow action by clicking the padlock next to the username field.
This way the credentials can be managed centrally.
The PDF needs to be updated and specify that the parent workflow is a site workflow. Some new comers don't know the difference between and list and site workflow.