The different turn speed beween the front and rear diff (while turning the vehicle) would create a really high torque between the front and rear diffs. I currently have my transer case and gearbox disassembled and I am not that impressed with the strength of the mechanism that engages the front driveshaft with the rear (in the transfer case).
I would quite confidently say that by driving a part time landcruiser in 4WD on a high traction surface that you would most likely break something, greatly accelerate wear, or cause damage by poor handling resulting in an accident.
I know that if I leave my landcruiser in 4WD on a good surface (dirt road) for too long then it binds up enough to make it difficult to disengage 4WD (even before I fitted the lockrite in the front). This is why manufacturers fit centre diffs to full time 4WDs (but also because without one it would be quite dangerous to drive).
I have heard of people trying to spin their tyres on the road and end up breaking an axle. So if you get the huge binding torque between the front and rear diffs (especially during a tight turn) then I believe that i is quite possible that something would break (or at least get badly damaged, and weakened), probably in the transfer case.
My landcruiser is 19 years old and had 503000 km's on it, so I definitely wont be trying it.
Andrew7lk: an open diif doesn't mean that you would only have one tyre turning! An open diff doesn't allow one axle to slip. The slip only happens if one tyre loses traction. If both tyres have good traction then it would take a lot of torque/power to make the TYRE slip. The diff only differentiates the speed between the two tyres. Now imagine that you have the traction of TWO tyres (fronts) trying to compete with the traction of the TWO tyres (rears) the amount of torque generated between the two axles. This huge twisting force travels through all of the uni joints, transfer case, etc looking for somewhere to release (hoping for a tyre to slip).
The amount of wear in the drivetrain would make little difference (a quarter of a U-turn, maybe?).
I read where people say that leaving a front air-locker locked can make it difficult to turn on loose surfaces (and dificult to steer on hard surfaces). Very few people would recommend doing this on a tarred road due to the damage it may cause (likely to cause). Now, that is just one tyre competing for traction with the other tyre (over a relatively short distance - the track) through a nice strong diff.
Now add the extra leverage between the front and rear diffs (wheelbase) and competing traction between PAIRS of tyres that is only going through the flimsy (compared to a diff) 4WD mechanism in the transfer case!!!
