In the past I’ve been asked to explain the meaning of “all y’all” (or “all of y’all” if you’re feeling fancy).
“All y’all” is the Southern Inclusive Plural — specifically, it means *all of you* as opposed to “y’all,” which just means “you plural”.
“Do y’all want to go to the movies” means “Do you plural want to go the movies” and *doesn’t* require everyone’s response. “Do all of y’all want to go to the movies,” on the other hand is asking if there’s a *collective desire” to attend the movies.
In my experience “all of y’all” is particularly useful when, for instance, you’ve come to a large gathering with a small group of friends. You don’t know everyone, but you want to indicate that everyone (even those whose acquaintance you haven’t yet had the pleasure of making) is included in an invitation.
We’re going to walk over to the park to see the movie. Do all of y’all want to come?
The converse is equally useful:
When speaking to one’s family and requesting departure from a large gathering: “Are y’all ready to leave?”, meaning not “is everyone at the gathering ready to leave,” but just “are you, my near and dear ones, ready to go?”
(“All y’all” is written as such, but pronounced “alla y’all”. This oughtn’t be surprising, as much of Southern would look the same if written phonetically ;-)