Its just a selection method. Your normal low range without the front axle engaged. Offers lots of advantages were traction is not the problem, its maneuverability, and slow speeds.
Not being in 4wd helps turning radius, and rolling friction.

Also helps with towing and starting out on hills, or positioning a trailer in a tight spot.

 

i agree, this is useful occasionally, if i want a low crawl speed while in 2wd.

i've used this to do engine braking on a steep downhill incline, or if i just want to keep the rpms up high at low speeds, so i don't have to work the clutch a lot to prevent stalling.

of course, i'm CERTAIN that my hubs were serviced recently and they're in FREE when i do it.