It is not a good idea to let anyone drive your vehicle if you do not have at least the state's required minimum car insurance coverages on it for a variety of reasons.

First normally another person's insurance is not going to cover your car if it is in an accident if you do not have primary insurance on it yourself. Also state laws differ however typically when you are stopped and required to show proof of insurance it needs to list the vehicle that you are driving for law enforcement to know there is insurance on it in case of an accident.

Most states require you to carry insurance, or another form of financial responsibility, on your vehicle to keep your registration current. If you have a lapse in car insurance some states have penalties such as registration suspension, the car owner's license suspension, fines, etc so there may be an issue with your vehicle even having valid registration to drive on the roadways if it is uninsured by you. If your state does not impose these penalties but requires vehicles to be insured than it will need insurance on it by you and a state will not usually accept insurance from another person that does not have the car listed on their policy as proof of insurance.

If a person that drives your car has insurance that would cover them in your car that coverage would be secondary to insurance you, the car owner, should have on the policy. This is referring to their Liability coverage and it is secondary in that if your Liability coverage was exceeded their insurance may help with the amount of claims above your limits for those they damaged while driving your vehicle.

A person's physical damage coverages, Collision and Comprehensive, do not generally extend to your vehicle when someone drives it. These coverages usually only cover a person's own vehicle, not other vehicles that the policyholder may drive. This is for many reasons but one main one is they are paying premiums for the type of car they drive and insurers don't want to cover a different type of car for example the policyholder may drive and insure an Escort and then borrow a Mercedes and wreck it. The person is not paying premiums to pay for repairs on high end car so their insurer would not want to cover damages to it.

If someone drives your car while it is not insured by you then normally both you and the person you allowed to operate the vehicle could face penalties. If a person was in an accident both the driver and you as the car owner could be held responsible for the damages the driver caused.

Your Department of Motor Vehicles can tell you about your state's insurance requirements and the penalties for allowing a car without insurance on the roadways.