they straighten them so that when they are chromed, they are, straight! same concept as painting over someone elses body work and trying to have a good representation of your work. We use Sherms plating in california, and typically, they get the bumper first to strip them and straighten them, then send it back so i can fir it to the car, and since we do "custom" work, it gets sectioned and tucked into the body, all the bolt holes welded up, etc...then sent back to sherms. the cool thing is that before the bumper gets touched, it is fit to the car, and i make adjustments, and they make a pattern of the bumper so they have the correct contour of it, etc... so when it's done, we all know it will still fit. sometimes it just takes quite a bit more communication with the chromer so that you're on the same page as them, otherwise, you very well might get a bumper back that doesnt fit anymore!