Sequence when tire traction fails is 2WD to 4WD to 4WD with differential lock to everything plus FEL (as, for instance, you're stuck in mud) to "find a neighbor with a tractor or large pick-up to pull you out". As to the differential lock, I use such only when going straight (or nearly straight) forward and backwards. Doing otherwise places a fair amount of pressure on the rear axle and differential, which, of course, is why use of the differential lock is not recommended on cement or other higher traction surfaces, and why it tears up the ground under the "inside" tire on a turn.
If you want to use the differential lock full time, good luck, and let us know how it turns out after a few hundred hours of use.
If you want to use the differential lock full time, good luck, and let us know how it turns out after a few hundred hours of use.