In my opinion, a category was left off: nowhere. I haven't used a coupon in over 11 years, because there aren't coupons for the things I use. By shopping using price per unit and cost per serving, I save MUCH , MUCH more than with any coupon!
If you look carefully at the things on coupons, you'll notice that they're usually for the MOST EXPENSIVE version of something, whether it's cleaning your windows (easily done with vinegar and water), doing laundry (easily accomplished with soap at .02/oz. or less), mopping your floor (not everyone needs a Swiffer now, do they?), polishing your furniture (a dab of cooking oil on a rag works just as well), or eating breakfast (cold cereal? Puleeease!)--the list goes on.
Coupons are enticements ro get you to buy stuff you don't really need--this means MARKETING TOOLS, and we all hate marketing, right? So why subject yourself to the most obvious form of it? I know why--convenience.
My price book (which I have recently brought out of the closet and reactivated) is my best "coupon" as far as discounts go. Just yesterday, I managed to save a hair over $24 on store-discounted berries (@4/$5) and broccoli (@2/$4). A week before that, I managed to save $6 on store-sale toilet paper($2 off their regular price). Watching the flyers, going to store websites, and closely watching (and recording) register receipts, I manage to save more money than any old coupon could save me, plus I have a record of where to go next time I need more.