I'm not going to argue that you don't need to mark the white wire, but what is the point?
10/2 Romex: 1 wire is white and one is black.
what's the point of marking the wire? to prevent what?
I too do not see the point; other than following code. The code is slowly becoming , DIY. When I started, if you saw a 10/2 wg on a 30A breaker home run or 10/2 wg into a water heater you kinda think 220Volt or meter it. If you see a white wire nutted with black, red, at a switch or any where think switch leg untill you find what it is.