“Smart Folders use Spotlight to dynamically update their aggregated content, based on search criteria that you specify. Think of Smart Folders as saved instances of a Spotlight search, because that is exactly what they are,” Anthony reports. “This means that you can create a folder to show anything from all the music or Word documents on your Mac, to something very specific like showing you all the image files that you have downloaded to your Downloads folder and marked with a file label color, but only within the last week. And because Smart Folders aren’t actually moving or copying any files on your Mac — they are dynamically showing the results of the search criteria you specify for them — they take up practically zero disk space.”
Read more, including step-by-stpe examples, in the full article here.