It is a lot cheaper for Diapers, Milk, Bread, eggs, tissues and rolls, even the wine i like is cheaper (Kim Crawford Sauv). Even one off purchases are cheaper like tires, TVs, pianos. And I get money back with Amex and executive membership. The fact they make their money from the membership shows how that they cut prices to almost cost.
Finally, like Trader Joes, they treat their worker very well. Vons and Ralphs seem to be at constant war with their employees.