You are developing a flat file data object and you need to change all the precision values to 10. Instead of changing each field individually, you make global changes through Excel.
You copy the metadata from the Developer tool into Excel, make changes to it, and copy it back to the flat file columns in the Developer tool. By using Excel, you avoid having to change each field individually.
The following image shows the process of moving a flat file to Excel, using Auto Fill to change certain values, and then copying the metadata back to the flat file data object in the Developer tool: