The service shows users available parking inventory on a map, and lets you book a spot online. They guarantee that if you book a spot, it'll be there. According to their website, each lot owner they partner with provides inventory data to avoid overbooking. Lot operators can post their spots without charge; SpotHero takes a commission whenever someone books one.
Whenever the topic of parking comes up, it's always more emotional than factual. Inevitably people don't realize how much parking is actually available in a place, or what the utilization is. It's frankly amazing in this day and age how little raw data we have about parking and its efficient use. That's one of the primary revelations of Donald Shoup's work and his book The High Cost of Free Parking: he brings real-world data to the discussion.
No app or tech can be a be-all, end-all, but this one is very encouraging for those of us that feel we need to maximize our resources first and foremost, and use precious space efficiently. For the subset of consumers that's obsessed with parking, I'm sure it will be a hit.