If you send out a direct mail piece to your contacts (especially if it contains a special offer) you will need a way to track them to see how many people responded, so you’ll know whether your mailer was successful.
When you first create the mailer, be sure to add a code to the coupon included, or in the body of the email, such as “OFFER0409”. Then when your contacts bring the coupons into your store, or use the coupon code on your website, etc., create a new Group in Gladhandle with that offer code as the Group name. Then, voila! You will have a new Group defining exactly who responded to your offer.