Generally, anyone living in your house is typically covered when driving your car, unless expressly excluded on the policy.
Permisive use also also allows you to allow your friends or family members who don’t live with you to use your car.
Permissive use means that if you give another driver permission to take your car, they will be covered by your car’s insurance coverage.
So if you allow your roommate (who doesn't have car insurance) to drive your car to run an errand.
What will likely happen if there is a single-car accident causing moderate damage to your car while your roommate is driving is that the insurance of your car will cover such accident.