The diff
file describes the net changes across the total DB. You should expect changes to this file to represent intended changes to the shovel output. If you are performing a refactor, with no intended code changes, you should expect no changes to this file.
The csv
file represents all operations that were performed that resulted in a data update. This doesn't including touching a content item (only updating a timestamp), but does include wiping a field out and then restoring that field to it's original contents. It will also track id
changes.