Ok, here goes...
Maps - Apple Maps automatically syncs with your calendar and address book. It shows alternate routes and lets you choose, it shows traffic (without paying for premium connectivity). Apple Maps lets you share your trip/arrival time with others. CarPlay also gives you the choice of Apple Maps, Google Maps, Waze and others. (Tesla maps isn't bad, though, and it's the only way to precondition for super charging.)
Music - Tesla has Tesla music and Spotify. Both require premium connectivity. CarPlay gives you Apple Music, Spotify, pandora, Amazon music, etc, basically anything that has an app. If you already pay for an Apple Music (or other) subscription, why should you pay for Spotify, too? If you have libraries on your phone they are automatically included in CarPlay. Your libraries travel with you to whatever car you drive, including rental cars.
Messages - CarPlay makes it much easier to compose a new message and will automatically look up someone in your address book (works better than Tesla's seems to.) (Car play doesn't show you the text, which is nice on the Tesla screen but you really shouldn't be reading a text while driving, anyway.)
Podcasts - The TuneIn app frequently glitches and won't download podcasts properly. it randomly logs you out. It doesn't remember where you were in a podcast if you switch between two podcasts or even if you just go into the store and come back out. CarPlay does all of these, remembers your playback position across cars (because it's actually on your phone) and maintains any subscriptions you have. You can also continue listening to a podcast when you leave the car. You can also use just about any podcast app you want, not just Apple's
Audiobooks - Tesla has nothing. You can listen to any audio book you own via CarPlay.
All of these use cellular data which I'm already paying for; no extra charges. The other advantage which I alluded to above is consistency. If I move from one car to another, the CarPlay interface is the same, my playlists, podcasts come along and remember where I am, etc. If I get a rental car it doesn't matter - it's the same. (Tesla's interface is good- one of the best I've used, but most cars' interfaces are crap.)
I think that's it...