Benefit? A couple come to mind. 1 is weight. Blazers weigh a little less, helping speed and FOC. All be it minimal.

Second. Vane clearance. Sometimes it's difficult to get good vane clearance w/ a long vane.

Third. If you're using a whisker biscuit, they're the bomb. They are much more rigid than a standard vane and stand up to the abuse much better.

I use 4" vanes on my 3D arrows, and will have 4" feathers on my hunting arras.