From Reference Help:
The PersistenceManager constructor example you show uses this signature:
Visual Basic (Declaration)
Public Function New( _
ByVal pShouldConnect As Boolean _
This constructor will create a new PersistenceManager and optionally connect to the server if pShouldConnect is true.
DefaultManager provides an easy way of referencing your "default" PersistenceManager. If you have not explicitly constructed a PersistenceManager DefaultManager will implicitly call the default constructor upon first use. If you have constructed a PersistenceManager DefaultManager will return your first constructed instance.
You can also set the PersistenceManager to be referenced as your DefaultManager. Once set, the PersistenceManager you've indicated will be returned as the "default".
When using DefaultManager without having first constructed an instance with the connection and data source extension of your choice, you lose the ability to catch and diagnose any connection problems to your PersistenceServer, since Connect is called implicitly