Disc Brakes do have advantages but not enough advantages to void your warranty. From day to day driving, you don't "need" disc brakes but they are very nice to have especially in emergency braking situations. I came very close to slamming into a Prius that decided to make a very last minute turn in the rain, I can tell you if I had drum brakes that accident probably would've happened. But those disc brakes are extremely impressive and make the Focus stop on a dime.
2012 Ford Focus SE Hatchback Race Red. 203A Spec. Window Tint. K&N Typhoon CAI. FSWerks Race Exhaust. Weathertech Digital Fit Floormats. HIDs with Projectors. Build Date: 2/14/2012
Active Duty US Army. MOS 91E (Machinist). OEF Vet.