The bigger screen is nice. The integration is also nice. I can push a button on my steering wheel to activate Siri to tell it where to go. Music controls on the wheel also pass through to CarPaly. I have a low res auxiliary screen to display added data (oil temp, weather, etc) and the music option will display music track data from CarPlay as well.
So instead of trying to look at a tiny screen that’s clipped onto an air vent, I can use the screens and integrated controls, keeping my hands on the wheel and my eyes more in the road.
Also, the biggest battery drain is having the screen on. CarPlay allows me to have the screen on the phone off while still accessing all the data. With a wireless adapter, I can also leave the phone in my pocket, so I don’t need to set it up every time I get in the car or remember to grab it when getting out. So it feels more like the native experience of using the car.
With the exception of the screen size I can do all of that with my phone in a mount as well. But you shouldn’t be operating your phone while driving, not even with CarPlay. It’s illegal in many countries.