Do you need fenders? No. Would they make your commute more enjoyable? Probably. Would they keep you bike in better condition? Certainly. To me, the main advantage to fenders is they help keep your bike clean and prevent dirt, grime, grit, water, etc. from fouling up your drivetrain. Notice that I said "help." Fenders are not a magic bullet that will prevent you from ever having to maintain your bike, replace a chain, etc. However, they will certainly help keep your drivetrain cleaner, better functioning and long lasting.