Why would I use this tool?

Because you want to search an active MySQL database for a string and possibly replace it with another.

I use this script when moving a WordPress database from my local development server to a production web server.

The traditional way of altering a WordPress MySQL database is to export an SQL file, open it in a text editor and use search/replace to modify your string.

The problem comes when you have a large database file; some text editors will hang when trying to open, or work with, really large files.