A Class IV roof is one of many roofing materials that have been designated by Underwriters Laboratories, under UL2218, as an impact-resistant material. The roofing materials will qualify for discounts on homeowner's insurance premiums.
Be aware that some discounts will come with clauses or waivers that prohibit replacement for cosmetic damage.  For example, a metal roof with hail damage will likely not be replaced if it has not been penetrated.