There are many reasons why bowhunters go the route of custom string sets, but three are primary: 1. Your current set is more than two years old, or has nicks, frays or worn servings; 2. You need a non-stock bow string length to match your exact draw length when you are between cam or module sizes; 3. You want a complete back-up set shot-in before you head on a major trip. Other reasons .