Coupons Work --Even When They're Not Used: Data analysis of a 16-month field experiment finds that coupons -- whether used or not -- still increase awareness purchasing of a brand or retailer. 
The professors found that consumers  who got the coupons but didn’t use them still “typically increased  their purchases in the associated stores.” In fact, these consumers  accounted for 60% of the coupons’ “sales lift” — the additional amount spent on both promoted and unpromoted items.  Data analysis found that coupons — whether used or not — still increase awareness purchasing of a brand or retailer.