When I was a kid, my mom (bless her heart) was a devout sale/coupon shopper. She would look at adds from different stores close to our home and cut any coupons that *might* have applied to our purchases.
At the time, I thought nothing of it. Looking back, I can see that we made a number of unneeded purchases under the guise of a good deal. Indeed, this idea is pervasive in today's consumer market with the receipt from seemingly ever store indicating how much you saved on that trip at the bottom. However, if you have five intended purchases that will cost $20, and you buy 6 items for $25, I find it hard to believe that you "saved" $5 even if that sixth item was originally marked for $10.
The best way to save money is to keep it in your pocket, not to get a fraction of it back after the sale/coupon. After all, if you saved your two cents on that $2 purchase, you still spent money.