I'm not a Car Play expert, but I've used Android Auto a LOT and I believe they operate almost identically (as much as an Apple phone acts like an Android phone anyway).
Not all apps that work on your phone work on Android Auto, but there are plenty of options that do. I use a few apps to play downloaded music, podcasts, etc -- all of which you can fully control via the infotainment screen. Spotify, Pandora, etc all work great for streaming music.
XM specifically, I'm not sure -- but I would expect that they have an app and that it is compatible with AA/CP. It's not going to be streaming from satellites -- I'm sure it's a feed you stream via the internet, so if you're in remote locations without a data connection, you're likely SOL.
The biggest plus for CP and AA is navigation. Being able to have Google Maps right there on your infotainment screen, with all of your saved and recently searched locations and real-time traffic info is wildly convenient. I went to the trouble to retrofit an aftermarket unit into my 2014 Frontier because once I started using AA on my wife's Santa Fe I couldn't go back to sticking my phone in a suction cup thing on the windshield....