A coupon for a free appetizer is a great way to entice customers to sample your menu. Regular customers may take the opportunity to try something new.  If they like it, they may tell their friends.  Of course being a cheapskate and applying the free coupon to the lowest priced appetizer, such as a half order of bread sticks, may also result in customers telling their friends.  Why not create an experience worth talking about that benefits both you and your customer?