Police officers, as first responders, often play a vital role in personal injury claims. Police officers have the responsibility to document the physical evidence, the statements of the drivers and passengers and any eyewitnesses.
Often the mere presence of a police officer will scare the at-fault driver into admitting fault for a crash. Once confirmed and documented by the officer, it will be very difficult for the at-fault driver to later change his story (as frequently happens without a police officer at the scene).
The investigation by a police officer will always be important. Unfortunately, it is not always accurate, and for the innocent party, that can create an obstacle. Regardless, if you are in an accident, never be in too big of a hurry in that you agree to simply "exchange information" with the at-fault driver.
Take the time---call the police, and get the facts and the drivers' versions and admissions properly documented. It will very likely make it much easier for you to present your claim and get your damages paid for by the at-fault driver's insurance.