Wide tires are good for flotation on soft loose surfaces. Dunes,deep soft snow,bottomless mudbogs.
For narrow,steep,rocky trails with sharp sticks/limbs and pokey rocks, taller skinny tires present less area to contact said hateful objects. Wider contact patches,while in theory present more surface area for traction,also decreases the actual surface pressure that adheres the rubber to the obstacle.Wider tires also put more stress on bearings, ball and u joints, and steering components.

Going on 24 years of off-roading experience and watching fools tear their s--t up, I'll stick with skinny tires.

Here is some more on the subject...

http://www.expeditionswest.com/research/white_papers/tire_selection_rev1.html