I think the biggest thing for me is the navigation, even on short trips that I make every day. I actually use Apple Maps still even though Google Maps and Waze are there on CarPlay since last fall. Mostly because Apple Maps has learned my entire routine, and as soon as I get in the car it knows that on Monday mornings I drop my son off at my parents' house and then I go into work, but that on Tuesdays I drop him off at daycare then work instead. The destinations pop in on the screen as soon a I jump in the car and connect (my head unit requires it to connect via lightning, but some CarPlay units work wireless.)

The overall integration with my phone and Apple Watch is great too, for text messages, music, and navigation. I'm at the point now where I really can't go back to not having CarPlay.