As the article says,; “But, as things stand, there is some doubt about whether the large, unfolded display will be of much practical benefit to a typical phone-user.”
But obviously there are some uses for which a larger screen would clearly be beneficial. Samsung’s publicity video, for example, shows someone using the larger screen to view what appears to be Google Maps. And there are many games, of course, that could be much better on a larger screen. In general, it’s the same benefits as being able to use a tablet instead of a phone.