Typing your login credentials manually during development takes away your time and focus. If you make a lot of small changes and need to check them often, that's a lot of time spent on the login screen. Set up a breakpoint in Xcode instead and speed up your development time.
You use Xcode build configuration files to define all sorts of useful build settings. You can open them with different text editors outside of Xcode and all properties are in plain text. It's common to use them for managing constants across different environments.