If you have the watch it will gently tap your wrist shortly before each turn, and it displays the turn in a very clear, uncluttered way on the watch screen, which you can clearly comprehend without needing to take your hand off the wheel. I find this is great in rental cars if you have no phone mount nor CarPlay and you want to avoid needing to interact with your phone while driving.
(Edited to add: I just went for a drive and paid more attention to how I use the watch with Maps, and I don't take my hand off the wheel if I'm just looking at the directions. Rotating it towards me quickly is enough to get the screen to wake. I have the Series 6 where the screen only dims and hides dynamic information when 'sleeping'. Maybe older watches where the screen actually turns off & on have a higher threshold before they wake?)
This seems like the kind of thing that's great if the map data is extremely accurate, but far worse than the older style if there's any chance of mis-counting lights. Even hitting a glitch once (e.g. it says 2 lights when it's really 3) could hurt trust in the app's navigation a lot.
For example: turn right at the traffic lights after the next one vs “turn right in 500 meters.”