I found the Porsche Connect app to be pointless unless the car has Nav. As I recall, it can do a few things like schedule service but a simple phone call to a service center works just as well! I removed it from my phone.
The Porsche Car Connect app is useful for some things, but isn't a gotta-have item. If your car is in for service it can help you track progress in some cases. If you ever lend your car to someone or let a valet drive it, the app provides a way to track it. If you forget where you parked it (!) or if it is ever stolen the app can help track it, show you its position and monitor speed. It also reports some conditions about the car, such as tire pressure when you parked it, presence or absence of a battery maintainer during winter, whether a door is open or unlocked, how full the tank is, what its current driving range is. It's nothing you can't get just be being in the car, but sometimes it's nice to see a few things when you aren't.
The Good To Know app is useful for looking up some feature when you don't have access to your paper manual. It's good for getting a Porsche fix when you are bored in your office. How many times have your seen a posting in the Tricks & Tips thread for some "trick" that wasn't hidden at all but explained in full in the manual?
I also have the Christophorus app which gives me articles from the magazine. So far I have had zero motivation to read anything from it on my phone.