That's not all of what coupons are for.
They're also a form of advertising. If you give them out to an influencer in your niche who can bring you great customers, you can make a lot of extra profits.
Imagine you're making an app for managing hair dressing salons. If there's a particular Youtuber popular among hair dressing salon managers, you can do a deal with them where their viewers get 20% off on the first year of their subscription to your app, and the influencer gets an extra 3% of that revenue.
You do this because you expect that people watching that channel are already hair dressing salon managers, and hence are very likely to become big spenders with your company once they start using your services. It's a great deal for everyone.
Honey turns that on its head by indiscriminately offering that influencer's valuable voucher code to everyone, reglardless of whether they've seen any of their videos.