Every once in a while you have a 12GB MySQL export and you need to edit one line. Or at least I do. Let's imagine I forgot to skip a table on export and don't want to repeat the 12GB export. That would never happen, but let's imagine.
If you've ever tried to open a 12GB file in your favorite text editor, you've probably found it's no longer your favorite text editor. Suddenly your new favorite text editor is whatever can open that file without crashing, and ideally taking less than 20 minutes. Your new favorite text editor is Sed.