The driveshaft is often a source of vibrations, and when it's straight, balanced, and the pinion angle is set right, you can still get harmonic vibration at certain speeds due to the interaction of various parts' natural harmonic frequencies. I've always removed mine and chunked them. But, if I ever did again, I'd keep mine for a just-in-case kinda situation. It would've been nice to try reinstalling one when I was having vibration issues.