In Germany, most grocers have little leaflets where the majority of sales are announced a bit ahead of time.
Aldi makes a lot of consumer goods business with that, when they sold their first desktop in the mid-90s, all of them built by Medion in the UK, it was a huge deal with long waiting lines even before the stores opened and them running out of stock in a matter of hours.
OK, it's possible that there's a low-profile outlet for releasing news of upcoming discount periods, and I just don't know about it. However, I can list several effects of the sale that occur whether or not shoppers know about it in advance of coming to the store:
- You might choose to buy more of something than otherwise, since it's cheaper right now.
- As a special case, you might have planned to buy zero of something, only to increase that amount when you notice it's on sale.
- You might choose to buy a discounted item in preference to the non-discounted item you were originally planning to buy.
The fact that one $3 thing you bought was unexpectedly on sale but every time you go to the store you spend $200 on other stuff is a thing that the store is aware of.
Imho this is probably due to the fact that they make more than enough money during the sales periods.
If somebody shows up during the sales period, with the intention of getting Parmesan Garlic, they very likely will still end up buying another flavor even if Parmesan Garlic ain't in stock anymore.
This is easily justified if somebody went to the store just for the Triscuit sale.