It serves a useful purpose, but it’s not necessary. There are pros and cons to keeping it on. Pros: ✓ Safety: Protects you from flying debris ✓ Cuts string to the manufacturer’s recommended length ✓ Less string means less strain on your machine ✓ Keeps string from hitting fences, trees, and other objects Cons: ✗ Shorter string ✗ Less visibility ✗ Not as easy to maneuver