Using the app is simple: choose a place from the listings, go there, and get your first drink free. For users, it could be a good way to discover new places -- which is useful in Tokyo because there are so many! The appeal for bar/restaurant owners is simply getting more customers in the door, hoping that they stay to order more drinks and food after that first drink. And if Hooch's success is any indicator, they will.
Of course, here in Tokyo, you'll still be charged the otoshi or seating charge where applicable. So the "free" drink might not be completely free.
They're also running a pre-launch campaign where the first 3 months drop to 100 yen/month.