I'm sorry but this guy is barely close.
This is a typical U-Tube video done moderately well by an un educated person.
He is correct when he said as you lift or lower, you push the body out. That's where his correct information stops.
He stated that incorrect panhard length has no effect on the arms. This is incorrect. The trailing arms are rigidly attached (with bushings) to the axle and the body. When you move the body to one side, it twists these arms actually turning the axle slightly. This would be called dog tracking.
Adding in a proper sized panhard (adjustable) will align everything. That is until you hit a bump. Now the diff deflects to a side, If the suspension compresses hard then bounces up past ride height, the diff can actually point one way then the other
Using his picture, Imagine the axle moving up, the angle that the bar is at, will push the diff to the side, causing the rear to twist and dog track. This is more noticeable at high speeds. This action causes the rear to swing back and forth slightly. It feels like a gust of wind hit the back end.
The panhard MUST be as horizontal as possible to minimize this deflection.
How bad the deflection is, is based on the angle and length of the bar.
My TJ with a 4 inch lift (short bar) was almost undrivable over 60 mph. I found this out driving it home when i bought it. My cruiser was lifted 2" and I would feel it over 70 mph changing lanes to the right (body roll).
Some people don't notice it, some people accept it but don't know why. I assign this as homework in my suspension class. Its watching a lifted jeep on the freeway. Does the back end move back and forth on freeway bumps. If yes, the bar is out of align, if no, then its properly installed. This applies to almost every coil spring rear.