I like my phone charged when I arrive somewhere
I prefer not to see texts or emails flashing on the screen while I drive
I like the bigger screen
I use it in other countries where data rates are huge and dumping the whole of Oz & NZ maps onto my phone isn’t practical
I use it out of phone signal – a lot
If somebody else is driving I can still use m phone
Mine’s always charged when I get to my destination, it’s plugged into my car stereo.
When using the sat nav, you don’t get texts or emails
Mine gets used plenty of places where there’s no phone signal data
You can download maps for Aus and NZ for $37, and they’re device native, no network necessary, maps are stored on the phone, just like a regular satnav.
That’s using CoPilot Live, which is cheaper, and, AFAIK, just as good as TomTom.
It’s also less likely to get stolen through being left in the car, ‘cos you’re more likely to take it with you.
And you can use the phone as well, although if you use the phone a lot, then a separate unit might be better, but by and large, pretty much every one of your points is answered by using one device with CoPilot Live, or TomTom installed, along with whatever maps you need.
That’s iOS and Android.