Let's face it: Most genealogical records we deal with make reference to more than one person of interest. The typical birth record may name both the individual being born and their parents. The typical marriage record will name both spouses. The typical census record will name all the people living in the same household. While there are certainly records that refer to only one person (a photo of a single individual, many military records, possibly the tombstone, just to name a few), we are normally going to be dealing with a digital image of a document that pertains to more than one person.
And this means that we have an issue when it comes to naming that digital file and filing it in one of our folders.
At least, it's an issue if we have only one digital copy of the document. But in the modern world of cheap computer storage, why would we want to limit ourselves to a single copy? I can't think of a good reason, but I'd be interested in hearing from you if you can come up with one.
So let's go forward with this idea of having multiple copies of such documents. Two copies for a married couple (let's assume, just for the sake of argument, that we're not interested in researching the witnesses or the person who conducted the ceremony). Three copies for a birth (child plus parents, ignoring for now those records that also identify grandparents or godparents). And possibly many copies for a census record that identifies a large number of related people.
This means that each copy can have its own name, using the name of one of the people of interest, and that each copy can be filed in the appropriate surname folder (if you are organizing by surname folder, as I am now doing). And it means that an individual's folder can contain documents dated after their death, such as those where the individual is mentioned as a parent in a child's later death record, or where a father dies prior to the birth of their last child.