Most insurance companies' polices require the policy holder to notify them of any licensed driver in your household. If you have a teenage son or daughter that has received their license, than you should inform your insurance company so that they do not find out later and believe you to have misrepresented the licensed drivers in your residence.
According to the New York State Insurance Department, an insurer is permitted to consider all resident operators of an insured vehicle in rating of an auto insurance policy. This includes your child, even if he or she has only a learner's permit.
Insurance companies in NYS are permitted to use classifications that reflect a possible exposure for liability on the part of the insurer, in the event that bodily injury or property damage occurs due to that child's operation of the vehicle.
There is a limited use classification that reflects a reduced likelihood of an incident by a youthful driver due to being an occasional operator and it is rated lower than if that person were the principal operator. The NYS Insurance Department also notes that if children live away from home while attending school (over 100 miles) are generally eligible for a reduced rate.
So while your friend may be able to borrow your vehicle without being added to your insurance, household members with licenses usually do need to be added so that the person will be properly insured.