From Android development experience I was familiar with UI definition style in XML and how all the app resources are defined under the organized res-folder. Although it required thorough knowledge in the application code and the UI flow, I was happy with using the resources in Android projects and because of that it was a thing to miss while jumping into the world iOS and Xcode.
After a short while, I noticed a massive boost in UI development convenience when using storyboards. Here’s a pretty good tutorial on storyboards, scenes and segues. Storyboard provides a main application flow even if you’re not familiar with the app itself i.e it is developed by other developer. It’s a great way to organize the UI visually, with less code written manually.
As a side effect, if the iOS project is based on an old version of iOS, there is not necessary a storyboard and the UX side is built with code and xib-files, the idea being similar to Android with xml layout files. These older apps may require UI porting into storyboards, which doesn’t seem like a walk in a park.