I've been using Android Auto for two years in our 2019 Subaru Forester. For navigation, I think Google Maps and Waze are significantly better than my past experience with Garmin or stock systems mainly because of the real-time traffic data as well as points of interest and other information, like speed limits, speed traps, and potholes, to name a few. But of course it's also updated regularly for the latest road and map data at no cost. But all this does use mobile data. Of course, it works with downloaded maps if you don't need/want all those other features.
It also allows hands-free messaging, which is quite convenient. I also like to listen to podcasts and Pandora. But again, almost all of this uses mobile data. For me, it's worth it for things like starting and stopping exactly where I left off in a long podcast, etc. I do sometimes listen to my own music or downloaded podcasts, but honestly, it's just audio and doesn't seem to consume much data at all. So I don't sweat the data usage.
Anyway, I'm a huge fan of Android Auto. I'm sure Apple Carplay is similar. It makes no sense for each auto manufacturer to develop and maintain their own proprietary in-car experience. So I like the concept. The only problem I've ever had is with connectivity drops. These are easily solved by using an OEM cable or another really good quality cable. I'm looking forward to more cars having wireless connectivity, but that's pretty limited right now.