You'd have to have some sort of payment mechanism set up with the grocery store. Many people, myself included, are leery of automatic payments that can send their budget out of control by causing a purchase at an inconvenient moment when one of those surprising unexpected expenses occurs. I want to control when I make purchases, and how much is purchased, not just have the fridge order willy nilly things I might need to choose to do without for a few weeks while I catch up. This may not be a concern for well-funded tech geeks, but for the rest of the population it's a live issue.