Spotlight is nice to search files using keywords, but it doesn't let you associate arbitrary keywords to your files.
With Branding Iron, you will mark your files and make them easily searchable.
Imagine you want to label a dozen of files as belonging to "Project Brinkman".
The traditional way to organize them is to put them in a folder called Project Brinkman
But now, with Branding Iron and Spotlight, you can just mark them, store them in whatever folder or hard disk (for example, by category : Accounting, Budget, Engineering, Artworks, ...) and then create a Smart Folder called "Project Brinkman".
Automagically, your files will be here. You can move them, modify them, rename them. They will be marked forever.