It may make sense to add another driver to your car insurance policy in certain scenarios:

Your teen just got their learners permit. As your son or daughter learns the rules of the road, you'll likely want to add them to your car insurance policy. That way, if they get into an accident with the family vehicle, your claim may be covered.
A family member is moving in. Suppose a parent, sibling or another member of your extended family is coming to live with you. If they don't have a car of their own, or if they'll be driving the vehicles you insure, you may want to consider adding them as a driver onto your car insurance policy. Check with your insurance provider to see if adding an extended family member to your policy is an option.

When you add another driver to your policy, their information may affect your car insurance premiums. Things like their driving record, gender and age may factor into what you pay for your policy, according to the NAIC.