Strong vs weak IBOutlets

About a week ago I finished reading “iOS Programming: The Big Nerd Ranch Guide (5th Edition)” in which, in all of the examples @IBOutlet declarations were marked “strong” (no weak keyword)
Now I’m reading Chapter 5 of “Cocoa Programming” and I see that@IBOutlet is declared as weak.
Which one is right? What do you suggest?
Or is it different because this is OS X, not iOS ? Or because XIB vs Storyboards ? Or maybe because Cocoa book is older than iOS book and from what I’ve googled Apple had changed their recommendations on weak/strong outlets.

Maciej Wozniak