Heroku takes a time-based approach to its services and billing. The idea is that you pay for how many hours each dyno that you use has run in a given month, and every free account has 750 free dyno hours. If I only run one dyno all month, I don’t have to pay anything at all. And even if an app that I use was to get slashdotted or something similar that would generate massive amounts of traffic, all I’d have to do is run a command or two to scale things up. I could add a dyno or two and only run them for as long as the traffic was too hard for a single dyno to handle the traffic, then I could scale it back down and I’d hardly have to pay anything at all unless I used those dynos for quite a while. You only pay for what you use, and you aren’t obligated to use anything more than what you need/want!  -- Anthony Grimes