Regarding the rear locker, yes it can make a difference, but it’s not required for the way 95% of drivers who actually take their LR3/4 off-road. If you’re used to an open diff vehicle, the traction control completely overcomes the “lift a front and rear tire, stop moving” scenario.
While this is basically just a dirt driveway, it shows the system working compared to the setup in a 4-Runner. Yes, with a locker, there wouldn’t be all the wheel spin, but I doubt it would spin much with all terrains on it either.
Being realistic, unless your car is just a trail rig, you’re probably not going to push it to where a locker is NECESSARY, because of the possibility for damage.
I have already taken mine places many wouldn’t, and have no issue with scratching, dings, etc, but I’m not going to push my DD to the point where it’s likely to roll, tear a hole in the T-case or gas tank, intentionally force a door into a rock to make a passage, or get stuck it in water over the tops of the tires where its going to seem in and destroy the electrical systems.
Not saying some don’t actually use a locker, but it gets a little old seeing everyone that’s planning to drive down a national forest road assuming they need the HD package.