Binding Mode Redundant for ItemsSource

Was wondering whether I need to set binding mode on DataGrid columns. The answer is no:

there is no need for this to be TwoWay. ItemsSource bindings work by reference, so when Add/Delete/Edit takes place on an editable datagrid, the chages reflect back to the source observable collection automatically (inspite of the binding mode).

WPF-it http://stackoverflow.com/questions/7505487/refresh-datagrid-automatically-when-its-itemssource-changed