I have always crested my arrows because I like the looks of it. I don't think that I can see it in flight, but it sure helps me find my arrows when they have snaked under the grass or something.
But it does add weight and when considering Dr. Ashbys studies that show that we want most of the weight front of center, I can't help wondering if I wouldn't be better off with just a few nice cresting stripes rather than the whole dip.
I have done most of my crown dipping with fletch lack and it is pretty thick, maybe the water based stains some guys are using would be so light that it wouldn't make a difference. ???