Another thing that gets me sometimes is the supermarket promotions of "Spend $75 dollars and get $10 off your next trip" or other variations.  I'd like to say I use these wisely, but sometimes I catch myself going in for maybe $40 dollars worth of items and end up spending more than I planned to get the "free" ten dollars.

An example of promotional pricing is a typical "2 for 1" deal or a "Buy One, Get the Other at 1/2 Price" deal. This can be on any product in any supermarket department.

An example of loss-leader pricing is a significantly reduced price on a staple item such as a bag or jug of milk. The supermarket uses this discount on a much-needed everyday item to lure people into their establishment. They hope the customer will buy other items during their visit - hopefully regular-priced items with higher profit margins.

I purchase loss-leader items if I need them. I won't buy an item I don't usually use just because it's on special (unless I really want to try the product). 

Sometimes, I will buy a sale item that I wouldn't have otherwise purchased. Usually this would be something like a meat or seafood item. If I'm at the store and see that duck breast, or shrimp, for example, are on sale, then I'll buy them Otherwise, I probably wouldn't. And if some items are on sale, then yes, I'll stock up on large supplies.

I have to agree with the posts above. There are certain products which I seek out depending upon a sale price. Likewise, there are other products which I refuse to buy, even when on sale (like produce or bread). Some items sale prices are too good; and, like the other posters, I tend to stock up.

There is an important consideration here - apples or bananas will spoil after a certain period of time. I wouldn't buy large quantities of such items, regardless of the sale price, because I wouldn't be able to use a large amount before it went bad. Certainly the sale price would entice me to purchase my usual amount or perhaps slightly more, but not a great increase.

If the loss leader pricing means sale prices on non-perishable goods, I join post #3 in stockpiling as much as I have space to store!

Being on sale often causes me to give something a second look, and if the sale is good enough, sometimes purchase things that I might not otherwise purchase- just to give it a try.  Now, my better half often makes fun of me for buying in bulk if there is a good sale on non-perishable goods, but if something we use frequently is on sale I load up!

I will not buy a product simply because it is on sale.  However, if a product that I want is on sale, I will generally buy more of it.  For example, grapes are often quite expensive.  I typically do not buy them until the are put on sale as loss leaders.  But I would not buy, for example, asparagus even if it were on sale.