Your insurance score is calculated based on information from your credit report and determines if you're a low risk or high risk driver and determines your insurance rates.
The higher your insurance score the better as it means you're low risk and don't get into accidents a lot.
Also the better the driver you are the lower your insurance premiums will be overtime.
A persons credit information is very predictive of any future accidents or insurance claims, which is why Progressive, and most insurance companies, uses this information to help develop more accurate rates.