It's super-handy, but I don't own a car (and try to rent cars with CarPlay when I do drive), so I only ever use it when walking. And there it's really nice to be able to pull up my watch, double-check the street name - because Siri will have butchered it - and so on, without having to take my phone out of my pocket.
You can turn off turn notifications in the watch settings if its distracting. I find that I never look at the car screen and I miss turns and I have the gps audio muted to not interrupt my podcasts. The watch vibrating on upcoming turns is super useful to me.