The Splattering of Blood
The shape of the blood spatter is mostly used to determine the size of the hole the blood is forced through. With a smaller hole, the stream will be more powerful, but the spatter size will be smaller. This helps determine the size of the wound.
Size of spatter is similarly very useful. For one, blood, like all objects, picks up speed as it falls. Unless it is from a fall above 26 feet, blood's terminal velocity, investigators can pinpoint from what height it fell. This is useful, for example, when trying to determine whether a person was standing or lying down during an attack.
Investigators can also judge the energy used to force the blood into flight. This can help tell how forceful the strike was. The higher the energy used, the smaller the dots of blood will be.
It is also possible to judge from which direction the strike came, by calculating the angle of the blood's impact using trigonometric formulas.