CV's not spinning while going down the road is most of our main reason for it. Keeps the boots from shredding themselves. Also a much simpler system than ADD and pretty much bombproof.
So it's the same thing as what a normal 4runner with part-time 4WD does (except not automated), and 1 less failure point with the ADD potentially being an issue in the Auto-4WD world?
The only issue I can see with manual is you lose the ability to set 4WD on the fly for scenarios where certain parts of the road are icy or heavy with rain, but then after 2-3 minutes of driving you turn 4WD off. I find this to be a very convenient option.