I noticed today that a cereal manufacturer was having a deal where if you buy its particular brand of cereals you would get like a coupon good for buying an item from a restaurant. The value of it was about $3. So if you think about it, buying that box of cereal is a better idea if you normally go to that restaurant a lot. Many people think that way too and so what they do is stock up on the cereal.
It can seem a little excessive, but it does make sense in many ways. The only real thing that would truly be bad I think is if you are buying more than you would have normally spent otherwise. Or likewise, if the free item you are getting is not something you normally purchase then it is simply an extra purchase that costs you extra money.
A common example of this too I see are cereals that give away free movie tickets. Again, makes perfect sense if you visit the theatres often. Many times the coupons are on the package of the boxes. So an alternative too is you can simply sell the product cheap to someone else if it is too much for you and still come up ahead.