A Class 4 shingle is rated as an impact resistant shingle. Most insurance companies will give you a premium discount for installing a Class 4 shingle on your roof. Impact resistance has to do with the shingle’s impact resistance to hail. Class 4 rated shingles will typically last longer and will do better in a hail storm. Insurance companies like this because it means they are less likely to have to pay for hail-related damages.
Metal roofs qualify for Class 4 shingle discounts, but you typically have to sign a “cosmetic” waiver.