Originally I think it started as dipping or cresting your arrows. Many in my area dip the backs of their arrow white. It does two things, it helps you find your arrow after the shot and you can see the blood on the arrow from your stand to see what sort hit you made on the deer. Assuming you got a pass through.

At least that is what everyone has told me that uses them. I personally don't mess with it.

I see no purpose for them at all for target or 3-D other than they look cool (to some).

Paul