The first video explains differential locks. Basically with an open differential all power would be routed to a wheel that’s getting no traction (for instance if it’s on ice). A differential lock closes it, so it’s as if there were no differential, so both wheels on the axle will turn at the same speed. This is bad if you’re on a normal road (obviously, since that’s why differential were invented) but great in low traction environments like mud or ice.
Most off road vehicles have locking differentials.
Yep, until I'd done off-roading, I never understood why my uncle told me (when driving his vehicle, which had the ability to lock the diff) - "Never ever use this on pavement / normal driving". I obeyed him, but I always thought he was full of it, until I had the money & time & inclination to work on cars, and I learned what was really going on.
"Aaaahhhh... so that's why he told me that..." Thanks Uncle Bill!
Applying the brake on the slipping wheel is one half of traction control. Reducing the power going to the wheel is the other half. I accidentally demonstrated this to myself many years ago when my car suddenly was almost completely ignoring my throttle input for a reason I couldn't explain. It turned out I still had the parking brake on and when I went over a patch of ice and the car lost traction, adding more brake wouldn't do much, so it simply ignored my throttle. Because I wasn't moving more than about 5 miles per hour to begin with, it felt like the car just refused to move, like a stubborn mule.
It is amazingly effective indeed. One time I was driving through ice and snow, and at the traffic light I turned of the ESP by mistake (was trying to plug in my phone charger in the lighter socket beside the button). When I took off I nearly crashed myself off the road, I never realised how slippery it was, and how much the car was covering for my ignorance.
Most off road vehicles have locking differentials.