Spoken directly to an individual, it's almost like the British concept of a corporation being a plural entity... "British Petroleum are" or "Ford are." The inference is you, and yours.
Spoken in the form of all y'all to a group of unrelated people, it's a recognition of multiple, plural entities. You and yours, plus you and yours, and you and yours, and so forth.
You are subconsciously being regarded as something of a representative of more than just yourself. It's almost always family related, but can also mean your coworkers, your friends, those who share your political beliefs or any other form of recognizeable bond. You and your affinity group would be all y'all. You have something in common, and are being addressed in common.
I realize this is a sort of high-falutin' description of a very humble, dialectical term, y'all, but does this make it make more sense, lol?
Seems to make more sense is a good way of putting it, as it is not yet crystal clear. I’m strugging with it. Not have it as part of my vernacular, it is hard to appreciate exactly what it means. You gave me a sense, but I would have to live with it a while to get the context. Thanks for trying.