From my racing experiance, I have found that the bumper serves an important purpose for the car on older chassis'. As the chassis on the car wears out, the rear holes become more elipsed, and it becomes easier to offset the rear toe block with slight taps. Although I do like to have the ease of this disassembly, I would rather prefer a non tweak rear end/front end. Up until just recently, I stoped doing this "mod" because my chassis is starting to wear.