Blood Splatter Lab

During this lab I was surprised to find that it seems to me that blood splatters cannot be used as evidence in a crime.  I came to this conclusion because in many of the graphs of blood splatters that I saw, there was not a clear trend of the relationship between the height of the drop of blood and the diameter of the the splatter.  I think you could see how long the blood had sat there, the general area of where the crime happened, and the DNA (which may lead you to a person).  However you can't tell much about the nature of the wound or weapon.  Another reason is not all wounds are the same size so you can't find height based on diameter of splatter if some splatters are from more blood or less.