Besides causing erosion on the mountain another reason to not leave the trail is snakes. Specifically timber rattlers!!! We saw one cross the trail in front of us, then once it got down in the leaves off the trail you couldn't see it. But, we heard it rattle. Not something I would want to step on off trail.
There are places that you can leave the main trail and take "shortcuts"from one level to another! DO NOT DO THIS---my head was bitten off by some very rude rock climber who apparently thought it was HIS set of rocks and not everyones. He said that shortcuts can cause erosion on the mountainside. He is probably right but his attitude was definitely wrong. What an idiot--it was the only damper on the trip.