All about preference. Old tutorials (before the storyboards were introduced) will tell you about using XIB files, however the storyboard can be used as a complete replacement for XIB.
If you prefer to use XIB, you can stick with them. The storyboard is just like the XIB group on the same page, which eliminates the number of files that you will have in your project.
Using storyboards will change some of the methods you need to use in the View Controller class, for example
-(id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
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