Well first off all you need to answer few questions. How much do you have invested in your project, are you and your staff certified and licensed (if applicable), how long have you been in this business, what is your accident history, have you ever been sued, how much would it cost to replace something that one of your men might destroy in the course of business, etc.
Sometimes insurance is to much expensive, you need to talk to attorney, that cost lot of money, so analyze your risk and cost and then decide for insurance.

so you just need to decide that does insurance cover your damages and you have enough profits?