Shall we always use [unowned self] inside closure in Swift

Question

In WWDC 2014 session 403 Intermediate Swift and transcript, there was the following slide

Answer 1

If self could be nil in the closure use [weak self].

If self will never be nil in the closure use [unowned self].

The Apple Swift documentation has a great section with images explaining the difference between using strong, weak, and unowned in closures:

https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/AutomaticReferenceCounting.html