What is the Diff with or with out rear loc-r?

[H3 Hummer]

I am not sure if this is true but the Hummer trainers said that you couldn't do something like the picture if you don't have a locker. I think your wheels would just spin when up in the air. With the locker it only gives power to the wheels on the ground. Sometimes only two.

I could be confusing technologies though.