its only done IF the drive shaft dose not have markings to line up (i.e. arrows etc) or a spline that stops you placing it in the wrong way, if you havent pulled the shaft apart yet and you didnt have bad vibes befor then dont do it, as it would have been balanced at the factory how it was, if you need to pull it apart put your owne markings on it prior to taking it apart to make shore you put it back how it was.
also check the bolt that holds the flange on the bell housing is not lose, as thay sometimes come lose and cause play in the flange etc, use thread lock
also check the bolt that holds the flange on the bell housing is not lose, as thay sometimes come lose and cause play in the flange etc, use thread lock
