Is this true and if so why do we have 4wd or All Wheel Drive?

The person that said that is confusing traction/tractive effort and friction. Tractive effort is what is used to rate the pulling capability of a locomotive. Its the force the locomotive can apply perpendicular to the track to move the train.

If you distribute the forces moving the truck over more tires with 4x4 then you can generate a higher tractive effort.

4x4 also helps ensure that, if one tire is on a very low friction surface like a sheet of ice, the other tires one higher friction surfaces can still provide traction/tractive effort of the tire with more traction.

 

4WD can allow quicker/shorter stops. There’s a reason Audi had an ABS off switch back in the 80’s. Team O’Neil has some great videos explaining this stuff, here are two.

https://www.youtube.com/watch?v=EMnT1gCYjP8

https://www.youtube.com/watch?v=5c2LMp4MUJU

 

Poetry.