Non owners insurance provides liabality coverage for vehicles not owned by you. If you don't own a vehicle, but want to make sure you are legal to drive and have liability protection for when you drive a vehicle not owned by you.
You drive a friend's vehicle who does not live with you. Your friend's auto insurance is limited and does not extend coverage to other drivers.
Your driver's license is suspended because of a DUI, and DMV requires you to get an SR 22 filing with your auto insurance, but you don't own a vehicle.
You've had accdient without insurance, and the DMV requires you to file either an SR 1P or SR 22 with your auto insurance, but you don't own a vehicle.