It’s a feature to exercise the whole display stack at every update, to make sure it works, for example when running remote desktop (or any other similar protocol/stack like citrix), where you can observe if the network still can send packets every second. Otherwise you need to wait a minute before noticing connectivity issues. Both rdp and citrix are extremely fragile and a clock that updates every second is a very good visual indicator for monitoring the connection. https://xkcd.com/1172