normal crime scene always have some type of evidence, wether it be fingerprints, bodily fluids or skin/hair, broken or misplaced objects... mainly things that can help point to the criminal. Scenes that have been on fire, or were burned down, exploded, etc. have little to no evidence. Many things are destroyed, and it can be dangerous. This is why procedures are different, because the state of the crime scene always changes how law enforment approaches the scenario. Best of luck to you!