Maybe my Dodge dealer could have used one to tell me my O2 sensor were bad on my Dakota after I told them three times to replace the OS sensor which they wouldn't because it didn't show up on their diagnostic reports. A week later when they finally replace the O2 sensor the car ran fine.
Too bad it doesn't go back to 89, but for anyone with a newer vehicle, it would be nice. From what I heard, it can give you an average estimate on how much a repair would cost, so you would know if the shop your car is at is trying to rob you.