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

According to Apple-doc

• Weak references are always of an optional type, and automatically become nil when the instance they reference is deallocated.

• If the captured reference will never become nil, it should always be captured as an unowned reference, rather than a weak reference

Example -

    // if my response can nil use  [weak self]
      resource.request().onComplete { [weak self] response in
      guard let strongSelf = self else {
        return
      }
      let model = strongSelf.updateModel(response)
      strongSelf.updateUI(model)
     }

    // Only use [unowned self] unowned if guarantees that response never nil  
      resource.request().onComplete { [unowned self] response in
      let model = self.updateModel(response)
      self.updateUI(model)
     }