An adjustable panhard rod simply allows you to centre the diff. It moves to one side slightly as you lower it and can cause clearance issues. I have never used one since clearance hasn't been an issue.
As for the others, nothing is "absolutely necessary" yet they can be used to improve things. I'm sure the internet is full of info (and misinformation) regarding their use, but as I understand it they both try to return the position of the arms (lower control arms and trailing arms respectively) to their standard angle even though the car is lower than standard.