I find it extremely dangerous if issues arise rarely but not rarely enough stop thinking about them and not as rarely as you would think. Look at this terrifying example from [1]. How long do you have to look at this code to tell if there is a reference cycle or not?

    class ServiceLayer {
        // ...
        private var task: URLSessionDataTask?

        func foo(url: URL) {
            task = URLSession.shared.dataTask(with: url) { data, response, error in
                let result = // process data
                DispatchQueue.main.async { [weak self] in
                    self?.handleResult(result)
                }
            }
            task?.resume()
        }

        deinit {
            task?.cancel()
        }
    }

[1] http://marksands.github.io/2018/05/15/an-exhaustive-look-at-...