It serves two essential purposes in the Dynamo context:
- It wraps the element into Dynamo’s equivalent Revit wrapper class so if you output these entities they are usable with all other Dynamo nodes.
- It performs element binding which basically synchronises elements between Revit and Dynamo and provides Dynamo with the instructions on how to marshal the elements while its running and when you re-open your graph. @jacob.small went into the details here: Element Binding in Revit if you want to know more.