The GPX1.2 when used with the Garmin Zumo XT displays only the Via Points but you also get the full route based on the Shaping Points but they are not displayed on the Garmin Zumo XT map.
You get a visible countdown when approaching Via Points.
You also get full navigation directions for the complete route.
Using the GPX1.1 with the Garmin Zumo XT is similar to the above but both the Via Points and the Shaping Points are visible on the XT map.
Personally I never use Via Points as I prefer the simplicity of Shaping Points and 95% of the time I prefer to travel alone.
I never know in advance when I will get hungry/thirsty or need to stretch my legs.
As others have said Garmin have nailed it with the Zumo XT.