Workbook.save() is a method provided by the openpyxl library in Python that allows you to save changes made to an Excel workbook to a file. The save() method takes a filename as a parameter and writes the current state of the workbook to the specified file.

Saving changes to an Excel workbook is important when you need to persist data changes or formatting changes. For example, you may use openpyxl to read data from a file, perform some data processing or analysis, and then save the results to a new or existing Excel file.