I believe it has to do with where you can drink what you purchase. As said above, off-premises sales are generally bottle (although I believe they can be single serving) but must be consumed off the premises of the selling establishment. On premises are generally open containers/Glasses and under most local ordinances must be consumed in the selling establishment. Of course that is a "northern" way of doing things. I've never understood places like Texas where you have to buy a bottle and a membership to drink it. I also don't understand the "drive through" margaritas shops theysupposedly have in New Orleans.