With the setting InsertResults->True, all results of evaluation, including outputs, error messages and the results of Print and related functions are inserted into the notebook being evaluated by NotebookEvaluate.
With the setting InsertResults->False, the output cells which would normally be generated in the notebook are completely suppressed. Error messages and the results of Print and related functions are relayed as output corresponding to the input cell which initially invoked the NotebookEvaluate function.