The store name is used when the item is added to the cart and if you also enter a price a Purchase History entry will be made. The entry is given a date stamp and will appear under Purchase History on the that item's detail screen in the List and Cart views. Knowing the previous prices paid will help you to make smart purchasing decisions.
Both the price and store for the item may be added or edited under the List and Cart Detail Screen Edit view. Editing the price and or store will not change the purchase history entry. Currently there is not a way to edit the Purchase History.
Future releases of Prep & Pantry will introduce price history reporting and will be integrated with usage reporting as well.