I would guess it would keep any standard rectangular thing (videos, websites, apps etc) in the square part in the middle. The bottom could be reserved for app short cuts or home buttons, keyboard or something. Top could be for easy access notifications (you could read a full text and respond without closing the main thing you’re doing) or maybe a readout from an AI assistant.

Otherwise there are some benefits, it’s aesthetically pleasing, I bet it’s ergonomically nicer to hold, and the curved edges would make it structurally more sound, less prone to breaking.