I scan and manage a lot of PDF documents. When they are first created I put them in a folder where they can then be OCR processed, or not, depending upon their source. The next step requires YEP, I use YEP to view and then properly name each document. I often use it to combine documents, which may require me to find related documents in YEP. When I get some time, I move the processed documents into their final resting place (folders organized by type of document, subtypes, and years) in the hope that when I need to locate it I can find it even if I forget the name and/or unique keywords. I know YEP can do a lot more, but for this one task alone it's well worth the cost.
When I want to find documents, I begin with Spotlight, if I can't find it, I use a spotlight based tool to dig deeper, and lastly I look in my directories to locate the document. Having several different ways to locate documents makes it easier to find documents when I need them.
Someday I'll spend the time to see if something has been added to YEP that will help me be more productive, but until then, it's doing the job I purchased it for. Yes, it's a bit buggy, and some things just don't work as I expect them to, but I've managed to tame it for my needs, and I'm happy.