As long as I can remember buying in bulk was always a money saver. In school you learned how to calculate unit price so you can find out what size was cheaper to buy. Of course the caveat was that you needed to actually use all that was in the bulk size of you were loosing money. Like, in our house, this is ever an issue. When we buy our ketchup in pounds rather than ounces you know we don't have a problem using food.
However lately I have noticed the bulk items are not cheaper. For instance our orange juice for the 64 oz size is more expensive than 2 of the 32 oz size. Which is silly really because you are using that much more plastic. So companies got wind of people buying bulk to save money and reversed it. Of course people will get wise once again and start buying the smaller products, these companies don't give their clientele enough credit.
Another place this applies is the warehouse stores. If you can stock up during a sale at a regular grocery store than you will save money even over the warehouse prices. You aren't gonna find those sales all the time. So planning for meals is difficult if you aren't sure when you are gonna be able to get some items on sale. You can get, at a warehouse store, whole chickens by the pair. It will run you around $10. Or if you wait for a sale and stock up you can get 4 chickens for less than $10. Guess what I have 4 of sitting in my freezer right now? So we will be having a lot of chicken this month. Which balances out earlier in the year when we bought a bunch of roasts during the BOGO free sale. The good news is by the time you are sick of something its gone and you won't get to have it again for a year.