If set to true, the TreeView populates data at the hierarchy-level represented by the TreeNodeBinding object on-demand (when ...

If set to true, the TreeView populates data at the hierarchy-level represented by the TreeNodeBinding object on-demand (when the node is expanded), either by calling a service directly from the client (if TreeView.PopulateNodesFromClient is set) or by causing a postback to the server.  If set to false, the TreeView populates node data all-at-once, when the page containing the TreeView is first requested.