My friend John posted a quick rant about grammatical and semantic errors this morning, and it inspired me to do likewise.
One of the things that I appreciate the most about Southern vernacular is that we have a pronoun for the second person, plural: "y'all". It's actually a contraction of "you all" and therefore the apostrophe properly goes after the "y", indicating that the letters lost in contraction would go there. (Many people are tempted to write it "ya'll" which is not a word at all, but spell-checkers aren't smart enough to know the difference so they assume that the spelling is correct. It's not.)
The real benefit of "y'all" is the same as for any other singular/plural pronoun: it clarifies whether you mean just one person or a group. No one gets confused when I say, "they went to the store", thinking that I really only meant, "he went to the store". Likewise, when I say, "would y'all like to go grab some lunch?" then Harry, Lou, and Jim know that I intend for all four of us to go, not just one of them and me.
An aside: sometimes then non-Southerners get caught with this. They try to bring the "y'all" but they haven't fully grokked its meaning, so they'll throw out a "y'all" when they really just mean "you". Consider this post a brief tutorial for non-Southerners.
The market value of "y'all" is hard to estimate. For one thing, it prevents the linguistic train-wrecks that sometimes occur without a true second-person, plural pronoun. I've heard Midwesterners wrestle with the ambiguous "you" and words that have plural form but singular meaning, like "guys", resulting in awkward phrases such as, "I'm coming to your guys house for lunch." As far as I know, that means that I have a guy, and she will be at his house for lunch-- not that she plans to eat lunch with Marcie and me.
More importantly, though: the definitive y'all would remove a lot of ambiguity in Scripture, where the Greek DOES have a clear and distinct second-person, plural pronoun, but our English Bibles translate both it AND the second-person, singular as "you." So, for example, this leads to an American reading of 1 Corinthians 6:19-20, which says, "do you not know that your body is a temple of the Holy Spirit..." and the assumption is made that my individual body is a temple of the Holy Spirit, because I don't realize that BOTH of the pronouns ("you" and "your") are actually plural, even though the words "body" and "temple" are singular. But if it read "do y'all not know that y'all's body is a temple of the Holy Spirit..." then I might actually conclude something closer to what Paul meant: that it's not about my individualism, but the collective, cooperative gathering of the body-- also known as the local church.
(By the way, there are LOTS of passages in the New Testament that we read as singular and, thus, individual which are actually plural, like the example above.)
So we need "y'all". It's a more sophisticated use of language.