Room service and chatting with my guests are exclusively tied to the app. My TV didn't work a lot of the times too. So, that isn't always an option to check the menu and call in.
A lot of functionality is tied to the app where it would be more difficult to do in person. Ex. checking my bill statements, making/canceling restaurant reservations, asking for help from guest services on crew chat instead of waiting in line at guest services (the line was very long bc they changed our disembarkation times on the last day and ppl were freaking wild animals waiting in line to get flights changed), etc.