By looking at the white of the wrap, you can easily determind the kind of blood, or if it wasnt a good hit, other body matter, that is on the arrow.
Is it covered in bright red blood, maybe with some lung material on it? If so, it means a good hit. Dark red blood...might meant you hit the deer in the liver. Green stuff, slimey looking wrap with a tinge of funky odor too it? Means that most likely you had a gut or stomach shot.
I used to use dipped arrows, then went to wraps. I doubt I will ever go back, especially since I now make my own arrows.