Xcode’s ability to use external configuration files is an underappreciated feature, which makes managing settings easier, and makes it possible to manage complex projects rationally.
I would bet serious money that at least 50% of iOS developers do not understand what a "Build Configuration" is and I would bet even more money that 95% of iOS developers have never heard of (let alone used) Xcode configuration files.
If you have worked on an iOS project of decent size you will have experienced the pain of having to manage and review changes to Xcode build settings. By not using the Xcode GUI and instead moving all of these changes to
.xcconfig files you will greatly simplify the review process as well as have a better understanding of what build settings your app has actually changed.
Every single iOS developer should read this article and immediately switch their Xcode projects to use