Bravo for looking for knowledge on this important topic. I’m constantly horrified by the poorly secured loads I see on the road these days. I wish everyone cared as much as you do.
The engineer in me makes securing anything loaded in a vehicle a mental puzzle of forces and weight distribution. To my mind, the thing I see mostly under appreciated is the huge forces from rapid deceleration (breaking and crashing). Especially inside vehicles. I consider everything in the vehicle a deadly weapon and try to secure it so my family isn’t a victim.
My paranoia leads me to think first, how do I hold this thing in place so the load doesn’t shift while driving forces in all directions. Then, how is the system I just created going to fail in a crash or rollover. Then I modify the system. I realize to be practical there is no such thing as a failure proof system, it I’m not going to hurt someone because I didn’t spend 5 minutes trying to take as much care as I am able to secure something.
Although it goes beyond the requested topic, that is a very good advise with regard to the items in the vehicle. We overlanders often have a lot of small items in the vehicle (handheld radios, tablet, gps messenger, thermo mug, tool box and so on).
If these are just unsecured in the rig they just rattle around while driving and this noises are just a pain in the ass. But these items can fly around in the car or even become dangerous projectiles in case of offroad driving or in an accident. Please do not use for example a free passenger seat as a storage area for loose items, even if it seems practical at first sight. In this case it could also happen that you intuitively grab them when they slip from the seat, for example during a severe braking. And then you might lose control of the vehicle. So please pack even small items securely but still within easy reach.
Back to the roofrack. From my experience, roof loads should always be reconsidered because of the resulting deterioration in driving characteristics and the additonal height. The rig and especially the chassis/ suspension are extremely challenged by additional roof loads. Furthermore a high roof load can also demand a lot from the driver. Just think of off-road or in strong crosswinds for example. Yes, it looks kind of cool, but does it all really have to go on the roof? That´s the question from my point of view. If so, please take special care with roof loads and their effects on the driving physics and tie everything down very well and check it regularly while on the road.
@4wheelrunner By the way, I think it's great that you're thinking about this topic and asking questions here. There's just too much badly lashed cargo. And especially during the vacation season there's a lot of stuff lying around on the highway here, even things like bicycles, surfboards etc., because of inadequate load securing. That is very dangerous and doesn't have to be the case!
Safe travels.