It's especially critical to do this if you interface with any web services. I have an iOS app that talks to two external services that sometimes go down or subtly change their format without notice; eventually I made the app read a config file from my server with service URLs, data format parameters, and messages to show the user. When, like clockwork, one of the services started sending corrupt data after New Year's Eve, I changed the service URL to point to a manually corrected version on my server, added a message indicating that some of the data would be a few days old, and answered all the support emails. A week later the corrupt data had cleared, and I switched back to the original version of the config file.