Notebooking aka price journal

No I am not talking computers. I am talking about a small spiral notebook to keep prices in. When you are planning to go shopping write down what you use in categories meats, personal care, frozen, baking etc then write down how much things cost the next time you buy that item. Keep checking back and add price changes and the date so you know ok this item goes on sale every 12 weeks or maybe every 3 weeks and try to only buy when the price is at its lowest. Why pay $3.29 for an item you can get the next week for $2.49?