واو الحال

What's the function of وَ‎‎ in the saying: ‎كُلُّ عامٍ وَأَنْتُمْ بِخَيْرٍ‎‎‎?‎‎ It is a dubious one. Most grammarians say that you don't need the وَ and that it would be of better Arabic style to skip it! Let's see why.