The developer of Yep says "Photos have iPhoto. Music has iTunes. But when it comes to PDFs and other office documents, you're on your own."
This is true to some extent. Apple has never thought to invent a decent document manager, although as far as locating documents is concerned, Spotlight is more than enough for me. However, there's no doubt that a good document manager wouldn't go amiss and Yep does a pretty good job. Particularly if you're browsing through your documents collection or scanning documents for filing, Yep makes looking at them and managing them a much nicer experience.
When you open Yep, you're reminded this is only a 10-day trial and given a brief overview of the interface. Yep is supposed to auto-import documents on start-up but I found that for some reason, this wouldn't work for me. Once you do manage to import documents, you're offered an auto-tagging feature, which is immensely useful because it takes keywords to identify documents. I don't really see how this is any more powerful than Spotlight but still, it makes organizing files a lot easier. However, it really comes into its own when scanning documents. Yep can auto-tag documents with keywords so that even your scanned documents are indexable.
There are other options out there such as Papers, which do a good job of organizing documents but few do browsing and cataloging PDFs as well as Yep.
