If your state requires liability insurance, you have to meet that requirement in order to license a vehicle for on the road use. There is usually a specified minimum coverage that must be maintained to operate the car on a public roadway. As far as I know, coverage for collision and "other" damage, such as windshield damage, hail damage, theft, vandalism, flood damage, tree falling on the car, fire, and so forth that pays YOU for such damages are NOT required. Liability risks have little or nothing to do with whether the car is kept in a garage or other shelter or not. A garage might lower the risk of theft or vandalism.