We should really look at the definition of "digital coupon" in at least two different ways. A coupon that is redeemed through an online or in-app order, and a coupon that is redeemed in-store that lives on the user's device. These are two completely different experiences and cater to a dramatically different persona and audience. Each solves problems that occur in the different scenarios, and each can provide similar value propositions in terms of contextual relevance.
A digital coupon in a physical world has only begun to provide value to the user. Using contextual triggers like time of day, location, real-time updates, etc. all need to be strongly considered.
Additionally - a single use digital coupon that is tied to a uniquely identifiable user ID provides unprecedented value to the retailer on a consumer's buying behaviors. Then using that data to make each message even more valuable to the shopper -- that's the power.