WHAT: Smart collections are collections of reference files, gathered according to a stored search.
There are two ways to create a smart collection: By saving search results as a smart collection, or by creating a new smart collection from scratch.
WHY: Smart collections provide a way to save the results of a search and make it available to other users. Each time it is opened, the content of a smart collection is refreshed with files found to match the search query stored in its settings.
Like collections, smart collections are made up of reference files only.