One of the "getting your money's worth" moments at PubCon LV 2010 was when a speaker in the coupon business provided a brief overview of the best ways or reasons for "~doing coupons": Excess inventory? Coupon. Slow season? Coupon. Brand loyalty reinforcement / customer retention. (Buy product. Get coupon for next purchase.) Coupon. Etc.
I don't recall him being overly impressed with coupons as a (loyal/repeat) customer acquisition strategy, i.e., if that's what you're thinking will be the benefit the data doesn't support the inference.
I guess like everything else in business it's a case of "test . . test . . test", all the while probably "testing assumptions" - like "will this work as a customer acquisition strategy" or will most "coupon customers" be one-timers - and hopefully not going broke in the process. :-/.