Bird
Rest in Peace
How much slip? I guess you'd say none in the driveline to the differential, but as with any differential, there can be slippage of the individual wheels on the ground. Will it shorten driveline life? No more than any normal usage. Don't use 4WD on hard, dry surfaces where the wheels can't slip (in which case you wouldn't need 4WD anyway); otherwise don't worry about it, that's what it's made for.