An application you are not using no longer has to be deleted to be stopped.
Pausing scales to zero, and changes nothing else
Pause takes the app down to zero instances. Its configuration, environment variables, domains and attached volumes stay exactly where they are, and the address stays reserved.
Resuming restores what you had
Your scale setting is remembered rather than overwritten, so resuming brings the app back at the same instance count on the same address. Pausing is a separate flag for exactly this reason: it never touches the number you chose.
Available from the application in the console, or by asking Otto to pause an app by name.