Saving money at COSTCO is something that I often but still continue to reject.
If you have a large family, say 4 or more, I think the benefits of shopping at Costco may be very evident. Price comparison with other retailers often has Costco coming out the money saving winner. Price per unit, Costco wins almost everytime.
With a smaller family, a couple or a single person may not be beneficial as you end up buying far more than you can use or need.
Read a more detailed discussion at Budget Fashonista.