Hi Meenakshi,
1) If you create the node in Component controller, The life span of that node will be through out the webdynpro component i.e the node is accessable through out the webdynpro component.
2) But if you create the node in view controller, the life span of that node will be restricted to the corresponding view only i.e the node is accessable only in that correspoding view.
But it is better to create nodes in component controller/custom controller.
Hope this gives you idea and pls revert if you need any further information.
Happy to help you.
KH