This term is used to reduce the awkwardness that the less-educated among us have with the fact that the singular and plural form of "you" in English is the same. It is used by restaurant hosts/hostesses and servers relentlessly. A particularly vulgar aberration of an already bad-enough term would be to say "yous guys", which is often heard in Long Island. And then, there is the Southern aberration, "y'all" - an example of Southerns' unfamiliarity with the English language.
"Welcome to Applbee's; would you guys like something to drink?"