I think the reason you're not supposed to chain up the front on a 4x4 (if you only chain two tires) is because if the front has traction and the rear doesn't, then the rear is more likely to try to come around when trying to stop, like pulling ebrake.

Of course that could be a problem on a FWD too, but you need the chains on wheels that have power going to them too.


A locker is potentially harder on axle components because it can put 100% of the power (torque) to a wheel, whereas with an open diff, they usually will only see 50% or less because its usually either shared with the tire on the opposite side (equal traction), or it goes to the tire with the least traction.
So strength-wise, since the rear axle is stronger than the front, a rear locker would be best if you only have one.

However, I agree that just putting one up front should be fine as long as you don't drive stupid. That way you don't have to deal with it on the street when you're in 2wd, and as was mentioned there's more weight up there. That's how my 4runner was for the first year after I did the SAS until I saved up for a rear ARB.

You should also know that a front locker will make steering more difficult in 4wd (it wants to go straight). The huge payoff in increased traction is well worth it though.