If you have a non-selectable locker in the front, shifting from 4 low to 2 low will release all of the bind in the front end caused by the locker and turning.
On a trail that requires a lot of low speed driving you would cruise most of the trail in 2 low and save all of the strain on your front end. When you reach an obstacle that will require 4 low, you shift to 4 low and use both axles and lockers until you pass the obstacle. Then shift back to 2 low. That sort of makes your front locker "selectable".