Redeeming coupons may cause people to feel a "shame stigma" which will affect others around them in grocery store lines according to CBC News.
I know that sometimes people will try to find a coupon for every little thing, and spend oodles of time at a checkout. To me, that seems rather annoying (and if you take into account the time spent finding coupons, perhaps counterproductive).
On the other hand, I managed to purchase a flight yesterday (on Air Canada, sorry Jon) at less than half the price the same ticket has been going for the past month. That made me happy.