Lets you edit a list of file names in a text editor (or any other way), then paste the results into the program to apply chances.
If you are able to use the terminal but want to look at what you are doing before committing, this is just the thing. I wish there were more tools that sprinkle just a bit of GUI onto traditional CLI tools. Why not best of both worlds?
To get all the power out of this you need to be able to do sophisticated manipulations on the text files. However, it is useful without that. If you do not know terminal and aren't going to learn it today, this might be significantly faster than hand editing file names via the finder. You can use office application like Office, google docs, pages, numbers etc to edit the text if that's how you are most comfortable. Just be very sure to check no blank lines or anything get inserted when moving the text around.
Only improvement I can think of would be to add undo (maybe even persistent after app quit in case later you realize an error). There is a button that looks like undo, but it actually resets the session and commits whatever changes you have made. Don't press by mistake.