I did very extensive testing with this and I can definitively say that 0 either turns the feature off or sets it back to default. The issue with high threshold settings, or in this case the 0 setting is that there is no, consistent breakaway by faster players in the open field. I didn't start to see the breakaway until I had the threshold slider below 30. I didn't see accurate speed representation until around 20. I chose 19.
I do believe there are other factors playing into this game behavior... Fatigue is a big one.
Higher settings present major concern in that the faster players never seem to gain ground on a ball carrier in the open field, and instead just seem to run behind him.
I am baffled by the number of sets running these high threshold settings.